Imaging element, stacked-type imaging element, imaging apparatus, and manufacturing method of imaging element

ABSTRACT

An imaging element which is formed by sequentially stacking at least an anode, an anode-side buffer layer, a photoelectric conversion layer, and a cathode, in which the anode-side buffer layer includes a material having structural formulain which thiophene and carbazole are combined.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 andclaims the benefit of PCT Application No. PCT/JP2017/037573 having aninternational filing date of 17 Oct. 2017, which designated the UnitedStates, which PCT application claimed the benefit of Japanese PatentApplication No. 2016-244224 filed 16 Dec. 2016, the entire disclosuresof each of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an imaging element a stacked-typeimaging element, an imaging apparatus, and a manufacturing method of theimaging element.

BACKGROUND ART

The application of imaging elements to cameras for smartphones,surveillance cameras, rear-view monitors for automobiles, and collisionprevention sensors rather than only digital cameras and video camcordershas become widespread and gained attention in recent years. In addition,improvement in performance and diversification of functions of imagingelements have been achieved in order to respond to various applications,and imaging elements keep evolving. However, imaging elements usingsilicon (Si) as a photoelectric conversion material have becomemainstream. In addition, miniaturization of pixels for improvingrecording density has progressed, and the size of an individual pixelhas reached substantially 1 μm. The light absorption coefficient of Siis about 10³ cm⁻¹ to 10⁴ cm⁻¹ in the visible light range, and aphotoelectric conversion layer of an imaging element is normallypositioned at a place with a depth of 3 μm or more in a siliconsemiconductor substrate. Here, as the miniaturization of the pixel sizeprogresses further, the aspect ratio of the pixel size and the depth ofthe photoelectric conversion layer increases. As a result, light leakagefrom an adjacent pixel or light incidence angles are limited, whichleads to deterioration in performance of the imaging element.

As a solution to the above problem, organic materials having a highabsorption coefficient have gained attention. In other words,photoelectric conversion using an organic semiconductor material isperformed, rather than photoelectric conversion using an inorganicsemiconductor material. Such an imaging element is called an “organicimaging element.” The absorption coefficient of an organic material inthe visible light range is about 10⁵ cm⁻¹ or higher, a thickness of aphotoelectric conversion layer of an organic imaging element or astacked-type imaging element, which will be described next, can bethinned, and thus improvement in sensitivity and increase in the numberof pixels are considered to be possible while preventing false colors,and therefore development is actively underway.

Stacked-type imaging elements having spectral sensitivity correspondingto red, green, and blue which are formed by slacking a plurality ofimaging elements have been developed and gained attention. Astacked-type imaging element does not need a color separation opticalsystem and three types of electrical signals (image signals)corresponding to red, green, and blue are taken out from one pixel.Therefore, a light utilization rate becomes higher, openings becomewider, and thus a false signal such as moiré seldom occurs.

However, although there are a variety of problems in putting organicimaging elements into practical use, it is necessary to clarify criteriarequired for imaging elements with respect to various initialcharacteristics such as photoelectric conversion efficiency, darkcurrent characteristics, an S/N ratio that is the ratio of a brightcurrent and a dark current, afterimage characteristics, and heatresistance in the manufacturing process. In addition, varioustechnologies have been proposed to solve the problem of such initialcharacteristics.

The imaging element disclosed in Patent Literature 1, for example, isregarded as being capable of satisfying required external quantumefficiency characteristics while satisfying required dark currentcharacteristics by satisfying the conditions that electron affinity ofthe electron blocking layer is greater than the work function of theadjacent electrode by 1.3 eV or more, and ionization potential of theelectron blocking layer is equal to or smaller than ionization potentialof the adjacent photoelectric conversion layer.

CITATION LIST Patent Literature

Patent Literature 1: JP 2007-088033A

DISCLOSURE OF INVENTION Technical Problem

However, even in a case in which a material satisfying the conditionsdisclosed in the above-described patent publication is used for a bufferlayer on the anode side, the material does not necessarily reach thelevel of practical use of the imaging element, and in particular,improvement in the dark current characteristics that significantlyaffect the S/N ratio and afterimage (a phenomenon in which a signalremains even after emitted light or reflected light from a movingsubject disappears when imaging and thus the subject is illustrated asif it has a tail) characteristics has been strongly demanded.

Therefore, an objective of the present disclosure is to provide animaging element having excellent dark current characteristics andafterimage characteristics, a stacked-type imaging element and animaging apparatus having the imaging element, and a manufacturing methodof the imaging element.

Solution to Problem

An imaging element according to a first aspect, a second aspect, or athird aspect of the present disclosure for achieving the above objectiveis formed by sequentially stacking an anode, an anode-side buffer layer,a photoelectric conversion layer, and a cathode, in the imaging elementaccording to the first aspect of the present disclosure, the anode-sidebuffer includes a material having structural formula (1) in whichthiophene and carbazole are combined, in the imaging element accordingto the second aspect of the present disclosure, the anode-side bufferlayer includes a material having structural formula (2) in whichthiophene and carbazole are combined, and in the imaging elementaccording to the third aspect of the present disclosure, the anode-sidebuffer layer includes a material having structural formula (3) in whichthiophene and carbazole are combined.

Here, X₁, X₂, and X₃ in structural formula (1) and Y₁, Y₂, Y₃, Y₄, Y₅,Y₆, Y₇, and Y₈ in structural formula (2) are each independently a groupconsisting of an alkyl group, an aryl group, an arylamino group, an arylgroup having an arylamino group as a substituent, and a carbazolylgroup, and may or may not have a substituent, the aryl group and thearyl group having an arylamino group as a substituent are an aryl groupselected from a group consisting of a phenyl group, a biphenyl group, anaphthyl group, a naphthyl phenyl group, a phenyl naphthyl group, atolyl group, a xylyl group, a terphenyl group, an anthracenyl group, aphenanthryl group, a pyrenyl group, a tetracenyl group, a fluoranthenylgroup, a pyridinyl group, a quinolinyl group, an acridinyl group, anindole group, an imidazole group, a benzimidazole group, and a thienylgroup, and the alkyl group may be an alkyl group selected from a groupconsisting of a methyl group, an ethyl group, a propyl group, a butylgroup, a pentyl group, and a hexyl group, or a linear or branched alkylgroup.

In addition, here, Ar₁, Ar₂, Ar₃, Ar₄, Ar₅, Ar₆, Ar₇, and Ar₈ instructural formula (3) are each independently an aryl group selectedfrom the group consisting of a phenyl group, a biphenyl group, anaphthyl group, a naphthyl phenyl group, a phenyl naphthyl group, atolyl group, a xylyl group, a terphenyl group, an anthracenyl group, aphenanthryl group, a pyrenyl group, a tetracenyl group, a fluoranthenylgroup, a pyridinyl group, a quinolinyl group, an acridinyl group, anindole group, an imidazole group, a benzimidazole group, and a thienylgroup.

In the imaging element according to a third aspect of the presentdisclosure, the anode-side buffer layer can include a material havingstructural formula (4) or structural formula (5): in which thiophene andcarbazole are combined.

A stacked-type imaging element of the present disclosure for achievingthe above objective is formed by stacking at least one of the imagingelements according to the first aspect, the second aspect, or the thirdaspect of the present disclosure.

The imaging apparatus according to the first aspect of the presentdisclosure for achieving the above objective has a plurality of theimaging elements according to the first aspect, the second aspect, orthe third aspect of the present disclosure, and the imaging apparatusaccording to the second aspect of the present disclosure for achievingthe above objective has a plurality of stacked-type imaging elements ofthe present disclosure.

In the manufacturing method of an imaging element of the presentdisclosure for achieving the above objective, the imaging element isformed by sequentially stacking at least an anode, an anode-side bufferlayer, a photoelectric conversion layer, and a cathode, in which theanode-side buffer layer includes a material having structural formula(1), structural formula (2), structural formula (3), structural formula(4), or structural formula (5) in which thiophene and carbazole arecombined, and the anode-side butter layer is formed by using a physicalvapor deposition method.

Advantageous Effects of Invention

In the imaging element according to the first to third aspects of thepresent disclosure, the stacked-type imaging element of the presentdisclosure, and the imaging apparatus according to the first and secondaspects of the present disclosure, the anode-side buffer layer is formedof a material having structural formula (1), structural formula (2), orstructural formula (3) in which thiophene and carbazole are combined,and thus dark current characteristics and afterimage characteristics canbe improved at the same time. In addition, in the manufacturing methodof the imaging element of the present disclosure, the anode-side bufferlayer is formed by using a physical vapor deposition method, and thusthe imaging element can be further miniaturized. Further, the effectsdescribed in the present specification are merely examples and are notlimitative, and additional effects may be exhibited.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A and FIG. 1B are conceptual diagrams illustrating sectional viewsof an imaging element of Embodiment 1.

FIG. 2A and FIG. 2B are conceptual diagrams illustrating sectional viewsof an imaging element of Embodiment 1.

FIG. 3A and FIG. 3B are a schematic partial sectional view of an imagingelement for evaluation of Embodiment 1 and a diagram schematicallyillustrating the flow of holes and electrons generated fromphotoelectric conversion, respectively.

FIG. 4 is a conceptual diagram of the imaging apparatus of Embodiment 1.

FIG. 5A and FIG. 5B are conceptual diagrams of a stacked-type imagingelement of Embodiment 2.

FIG. 6 is a schematic partial sectional view of an imaging element and astacked type imaging element of Embodiment 3.

FIG. 7 is an equivalent circuit diagram of the imaging element and thestacked-type imaging element of Embodiment 3.

FIG. 8 is a schematic partial sectional view of a modified example of animaging element (modified example-1) and a stacked-type imaging elementof Embodiment 3.

FIG. 9 is a schematic partial sectional view of a modified example of animaging element (modified example-2) and a stacked-type imaging elementof Embodiment 3.

FIG. 10 is a schematic partial sectional view of a modified example ofan imaging element (modified example-3) and a stacked-type imagingelement of Embodiment 3.

FIG. 11 is a schematic partial sectional view of a modified example ofan imaging element (modified example-4) and a stacked-type imagingelement of Embodiment 3.

FIG. 12 is a schematic partial sectional view of a modified example ofan imaging element (modified example-5) and a stacked-type imagingelement of Embodiment 3.

FIG. 13 is a conceptual diagram of an example in which an imagingapparatus formed of the imaging element and stacked-type imaging elementaccording to an embodiment of the present disclosure is used in anelectronic device (camera).

FIG. 14 is a diagram illustrating a synthetic scheme of a materialexpressed by structural formula (4) forming an anode-side buffer layer.

FIG. 15 is a chart showing the analysis result of ¹H NMR of a compound(A).

FIG. 16 is a chart showing the MALDI-TOF-MS analysis result of thecompound (A).

FIG. 17 is a graph showing the absorption spectrum in a case in whichthe compound (A) is deposited on a quartz substrate to a thickness of 50nm and is converted to a thickness of 10 nm.

MODE(S) FOR CARRYING OUT THE INVENTION

The present disclosure will be described below on the basis ofembodiments with reference to the drawings; however, the presentdisclosure is not limited to the embodiments, and various numbers andmaterials appearing in the embodiments are examples. Further,description will be provided in the following order.

-   1. Overall description of imaging element according to first to    third aspects of present disclosure, stacked-type imaging element    according to present disclosure, and imaging apparatus according to    first and second aspects of present disclosure-   2. Embodiment 1 (imaging element according to first to third aspects    of present disclosure, stacked-type imaging element according to    present disclosure, and imaging apparatus according to first and    second aspects of present disclosure)-   3. Embodiment 2 (modification of Embodiment 1)-   4. Embodiment 3 (modification of Embodiment 2)-   5. Others    <Overall Description of Imaging Element According to First to Third    Aspects of Present Disclosure, Stacked-Type Imaging Element    According to Present Disclosure, and Imaging Apparatus According to    First and Second Aspects of Present Disclosure>

In an imaging element according to first to third aspects of the presentdisclosure including preferred modes described above, an imaging elementaccording to the first to third aspects of the present disclosureforming a stacked-type imaging element of the present disclosure, and animaging element according to the first to third aspects of the presentdisclosure forming an imaging apparatus according to the first andsecond aspects of the present disclosure (these imaging elements will becollectively referred to as “the imaging element or the like of thepresent disclosure”), the difference between the highest occupiedmolecular orbital value (HOMO value) of a material forming an anode-sidebuffer layer and the HOMO value of a p-type material (specifically, ap-type organic semiconductor material) forming a photoelectricconversion layer is desirably in the range of ±0.2 eV.

In the imaging element or the like according to an embodiment of thepresent disclosure including preferred modes described above, the HOMOvalue of a p-type material (specifically, p-type organic semiconductormaterial) forming the photoelectric conversion layer is preferably avalue from −5.6 eV to −5.7 eV.

In addition, in the imaging element or the like according to anembodiment of the present disclosure including various preferred modesdescribed above, carrier mobility of a material forming the anode-sidebuffer layer is desirably 5×10⁻⁶ cm²/V·s or higher, and preferably1×10⁻⁵ cm²/V·s or higher.

In addition, in the imaging element or the like according to anembodiment of the present disclosure including various preferred modesdescribed above, in order to prevent light absorption of the anode-sidebuffer layer from adversely affecting a layer positioned on the cathodeside in a case in which light is incident from the anode side, it isdesirable for a material forming the anode-side buffer layer topreferably have little light absorption in the visible light range, andspecifically, for an absorption spectrum of the material forming theanode-side buffer layer to have an absorption maximum at a wavelength of425 nm or lower, and preferably a wavelength of 400 nm or lower.

In addition, in the imaging element or the like according to anembodiment of the present disclosure including various preferred modesdescribed above, the anode and the cathode may be formed of atransparent conductive material. Alternatively, any one of the anode andthe cathode (electrode on the light incidence side) is formed of atransparent conductive material, and the other may be formed of a metalmaterial. In addition, in this case, the anode positioned on the lightincidence side may be formed of a transparent conductive material andthe cathode may be formed of Al, Al—Si—Cu, or Mg—Ag, or the cathodepositioned on the light incidence side may be formed of a transparentconductive material and the anode may be formed of Al—Nd or Al—Sm—Cu.

The imagine element according to the first aspect to third aspects ofthe present disclosure including various preferred modes described abovecontains a photoelectric conversion element.

In the imaging element or the like according to an embodiment of thepresent disclosure including various preferred modes described above, athickness of the anode-side buffer layer is not limited; howeverexamples thereof may be preferably 5×10⁻⁹ m to 5×10⁻⁸ m, or 5×10⁻⁹ m to2.5×10⁻⁸ m.

Specific examples of the imaging element or the like according to anembodiment of the present disclosure include an imaging element (forconvenience, referred to as a “first-type blue imaging element”) havinga photoelectric conversion layer which absorbs blue light (light of 425nm to 495 nm) (for convenience, referred to as a “first-type bluephotoelectric conversion layer”) and having sensitivity to blue, animaging element (for convenience, referred to as a “first-type greenimaging element”) having a photoelectric conversion layer which absorbsgreen light (light of 495 nm to 570 nm) (for convenience, referred to asa “first-type green photoelectric conversion layer”) and havingsensitivity to green, and an imaging element (for convenience, referredto as a “first-type red imaging element”) having a photoelectricconversion layer which absorbs red light (light of 620 nm to 750 nm)(for convenience, referred to as a “first-type red photoelectricconversion layer”) and having sensitivity to red.

In addition, an imaging element (an imaging element in which theanode-side buffer layer is not provided, or an imaging element in whichthe anode-side buffer layer is not formed of a material havingstructural formula (1), structural formula (2), structural formula (3),structural formula (4), or structural formula (5) in which thiophene andcarbazole are combined) of the related art which is an imaging elementhaving sensitivity to blue will be referred to as a “second-type blueimaging element” for convenience, an imaging element having sensitivityto green will be referred to as a “second-type green imaging element”for convenience, an imaging element having sensitivity to red will bereferred to as a “second-type red imaging element” for convenience, aphotoelectric conversion layer forming the second-type blue imagingelement will be referred to as a “second-type blue photoelectricconversion layer” for convenience, a photoelectric conversion layerforming the second-type green imaging element will be referred to as a“second-type green photoelectric conversion layer” for convenience, anda photoelectric conversion layer forming the second-type red imagingelement will be referred to as a “second-type red photoelectricconversion layer” for convenience.

The stacked-type imaging element according to an embodiment of thepresent disclosure includes at least one imaging element or the like(photoelectric conversion element) according to an embodiment of thepresent disclosure, and specific examples thereof include:

[A] the configuration and structure in which the first type bluephotoelectric conversion unit, the first type green photoelectricconversion unit and the first type red photoelectric conversion unit arestacked in the vertical direction, and

each of the control units of the first type blue imaging element, thefirst type green imaging element, and the first type red imaging elementis provided on the semiconductor substrate;

[B] the configuration and structure in which the first type bluephotoelectric conversion unit and the first type green photoelectricconversion unit are stacked in the vertical direction,

the second-type red photoelectric conversion layer is disposed belowthese two layers of the first type photoelectric conversion units,

and each of the control units of the first type blue imaging element,the first type green imaging element, and the second type red imagingelement is provided on the semiconductor substrate;

[C] the configuration and structure in which the second-type bluephotoelectric conversion unit and the second-type red photoelectricconversion unit are disposed below the first-type green photoelectricconversion unit,

and each of the control units of the first type green imaging element,the second type blue imaging element, and the second type red imagingelement is provided on the semiconductor substrate; and

[D] the configuration and structure in which the second-type greenphotoelectric conversion unit and the second-type red photoelectricconversion unit are disposed below the first-type blue photoelectricconversion unit,

and each of the control units of the first type blue imaging element,the second type green imaging element, and the second type red imagingelement is provided on the semiconductor substrate.

Further, the arrangement order of the photoelectric conversion units ofthe imaging element in the vertical direction is preferably the bluephotoelectric conversion unit, the green photoelectric conversion unit,and the red photoelectric conversion unit in order from the lightincidence side, or the green photoelectric conversion unit, the bluephotoelectric conversion unit, and the red photoelectric conversion unitin order from the light incidence side. The reason for this is thatlight having a shorter wavelength is absorbed on the light incidenceside with high efficiency. Since red has the longest wavelength amongthe three colors, it is preferable to position the red photoelectricconversion unit at the lowermost layer when viewed from the lightincidence side. One pixel is formed by the stacked structure of theseimaging elements. Furthermore, the first-type infrared photoelectricconversion unit may be provided. Here, it is preferable that thephotoelectric conversion layer of the first-type infrared photoelectricconversion unit may be formed of an organic material, for example, andis the lowermost layer of the stacked structure of the first-typeimaging element, and is disposed above the second-type imaging element.Alternatively, the second-type infrared photoelectric conversion unitmay be provided below the first-type photoelectric conversion unit. Thevarious second-type photoelectric conversion layers described above maybe formed on a semiconductor substrate. Further, a photoelectricconversion unit is formed by sequentially stacking at least an anode, aphotoelectric conversion layer, and a cathode.

In the first-type imaging element, for example, any one of the anode andthe cathode is formed on an interlayer insulating layer provided on thesemiconductor substrate. The second-type imaging element formed on thesemiconductor substrate may be a back surface illuminated type or afront surface illuminated type.

In the imaging element (photoelectric conversion element) or the likeaccording to an embodiment of the present disclosure, in a case in whichthe photoelectric conversion layer is formed of an organic material, thephotoelectric conversion layer may be formed in any of the followingmodes:

-   (a) a p-type organic semiconductor layer formed of a single layer or    multiple layers;-   (b) a slacked structure of a p-type organic semiconductor layer and    an n-type organic semiconductor layer; a stacked structure of a    p-type organic semiconductor layer, a mixed layer (bulk    heterostructure) of a p-type organic semiconductor material and an    n-type organic semiconductor material, and an n-type organic    semiconductor layer; a stacked structure of a p-type organic    semiconductor layer and a mixed layer (bulk heterostructure) of a    p-type organic semiconductor material and an n-type organic    semiconductor material; a stacked structure of an n-type organic    semiconductor layer and a mixed layer (bulk heterostructure) of a    p-type organic semiconductor material and an n-type organic    semiconductor material; and-   (c) a mixture (bulk heterostructure) of a p-type organic    semiconductor material and an n-type organic semiconductor material.    However, the stacking order may be arbitrarily switched. In    addition, one or two or more kinds of p-type organic semiconductor    materials or n-type organic semiconductor materials may be included    in the same layer. Not only two types but also three or more types    of semiconductor materials may be included in the bulk    heterostructure.

Although examples of the p-type organic semiconductor material includenaphthalene derivatives; anthracene derivatives; phenanthrenederivatives; pyrene derivatives; perylene derivatives; tetracenederivatives; pentacene derivatives; quinacridone derivatives;thienoacene-based materials represented by thiophene derivatives,thienothiophene derivatives, benzothiophene derivatives,benzothienobenzothiophene (BTBT) derivatives, dinaphthothienothiophene(DNTT) derivatives, dianthracenothienothiophene (DATT) derivatives,benzobisbenzothiophene (BBBT) derivatives, thienobisbenzothiophene(TBBT) derivatives, dibenzothienobisbenzothiophene (DBTBT) derivatives,dithienobenzodithiophene (DTBDT) derivatives, dibenzothienodithiophene(DBTDT) derivatives, benzodithiophene (BDT) derivatives,naphthodithiophene (NDT) derivatives, anthracenodithiophene (ADT)derivatives, tetracenodithiophene (TDT) derivatives, andpentacenodithiophene (PDT) derivatives (which will be referred to as“thienoacene-based materials represented by various derivatives” below);triallylamine derivatives; carbazole derivatives; picene derivatives;chrysene derivatives; fluoranthene derivatives; phthalocyaninederivatives; subphthalocyanine derivatives; subporphyrazine derivatives;metal complexes having heterocyclic compounds as ligands; polythiophenederivatives; polybenzothiadiazole derivatives; polyfluorene derivatives,and the like, among these, a p-type material (p-type organicsemiconductor material) having the HOMO value from −5.6 eV to −5.7 eV,for example, a thienoacene-based material represented by quinacridonederivatives or various derivatives described above is preferably used asdescribed above, and a combination of the anode-side buffer layer with amaterial having structural formula (1), structural formula (2),structural formula (3), structural formula (4), or structural formula(5) in which thiophene and carbazole are combined may be exemplified.

Examples of the n-type organic semiconductor material include fullerenesand fullerene derivatives <for example, fullerenes such as C60, C70, orC74 (high order fullerenes), endohedral fullerenes, etc.), fullerenederivatives (e.g., a fullerene fluoride, a PCBM fullerene compound, afullerene multimer, etc.), an organic semiconductor material having ahigher (deeper) HOMO value and lowest unoccupied molecular orbital(LUMO) value than the p-type organic semiconductor material, andtransparent inorganic metal oxide. Specifically, examples of the n-typeorganic semiconductor material include a heterocyclic compoundcontaining a nitrogen atom, an oxygen atom and a sulfur atom, forexample, organic molecules and organometallic complexes having pyridinederivatives, pyrazine derivatives, pyrimidine derivatives, triazinederivatives, quinoline derivatives, quinoxaline derivatives,isoquinoline derivatives, acridine derivatives, phenazine derivatives,phenanthroline derivatives, tetrazole derivatives, pyrazole derivatives,imidazole derivatives, thiazole derivatives, oxazole derivatives,imidazole derivatives, benzimidazole derivatives, benzotriazolederivatives, benzoxazole derivatives, benzoxazole derivatives, carbazolederivatives, benzofuran derivatives, dibenzofuran derivatives,subporphyrazine derivative, polyphenylene vinylene derivatives,polybenzothiadiazole derivatives, polyfluorene derivatives and the likein a part of the molecular skeleton, and subphthalocyanine derivatives.Examples of a functional group or the like included in fullerenederivatives include a halogen atom; a linear, branched or cyclic alkylgroup or phenyl group; a functional group having a linear or condensedaromatic compound; a functional group having a halide; a partialfluoroalkyl group; a perfluoroalkyl group; a silylalkyl group; asilylalkoxy group; an arylsilyl group; an arylsulfanyl group; analkylsulfanyl group; an arylsulfonyl group; an alkylsulfonyl group; anarylsulfide group; an alkylsulfide group; an amino group; an alkylaminogroup; an arylamino group; a hydroxy group; an alkoxy group; anacylamino group; an acyloxy group; a carbonyl group; a carboxy group; acarboxamide group; a carboalkoxy group; an acyl group; a sulfonyl group;a cyano group; a nitro group; a functional group having a chalcogenide;a phosphine group; a phosphonic group; derivatives thereof.

Although a thickness of the photoelectric conversion layer formed of anorganic material (which may be referred to as an “organic photoelectricconversion layer”) is not limited, examples of the thickness includevalues in the range of, for example, 1×10⁻⁸ m to 5×10⁻⁷ m, preferably2.5×10⁻⁸ m to 3×10⁻⁷ m, more preferably 2.5×10⁻⁸ m to 2×10⁻⁷ m, evenmore preferably 1×10⁻⁷ m to 1.8×10⁻⁷ m. Note that organic semiconductorsare mostly classified into the p-type and the n-type, and the p-typemeans that holes are easily transported and the n-type means thatelectrons are easily transported. The interpretation of organicsemiconductors is not limited to having holes or electrons as thermallyexcited majority carriers like inorganic semiconductors.

In addition, it is desirable for an absorption coefficient α of thephotoelectric conversion layer to be 1×10⁴ cm⁻¹ or higher, andpreferably 1.5×10⁴ cm⁻¹ or higher, and a molar absorption coefficient εof the photoelectric conversion layer to be 1×10⁴ dm³·mol⁻¹l·cm⁻¹ orhigher, and preferably 1.8×10⁴ dm³·mol⁻¹l·cm⁻¹ or higher. Furthermore,although the sublimation temperature of a material forming thephotoelectric conversion layer is not limited, it is desirably 250° C.or higher. Although the molecular weight of the material forming thephotoelectric conversion layer is not limited, examples thereof are 2000or lower, preferably 500 to 1500, and more preferably 500 to 1000.

Alternatively, examples of the material forming an organic photoelectricconversion layer that photoelectrically converts light of greenwavelength include rhodamine-based pigment, melacyanine-based pigment,quinacridone-based derivative, subphthalocyanine-based pigment(subphthalocyanine derivative), etc. Examples of the material forming anorganic photoelectric conversion layer that photoelectrically convertslight of blue wavelength include coumarinic acid pigment,tris-8-hydricoxyquinoline aluminum (Alq3), melacyanin-based pigment,etc. Examples of the material forming an organic photoelectricconversion layer that photoelectrically converts light of red wavelengthinclude phthalocyanine-based pigment and subphthalocyanine-based pigment(subphthalocyanine derivative).

Alternatively, examples of inorganic materials forming the photoelectricconversion layer include crystal silicon, amorphous silicon,microcrystalline silicon, crystalline selenium, amorphous selenium, anda compound semiconductor material including CIGS (CuInGaSe), CIS(CuInSe₂), CuInS₂, CuAlS₂, CuAlSe₂, CuGaS₂, CuGaSe₂, AgAlS₂, AgAlSe₂,AgInS₂, or AgInSe₂ which is a chalcopyrite-based compound, GaAs, InP,AlGaAs, InGaP, AlGaInP, or InGaAsP which is a Group III-V compound, andfurther CdSe, CdS, In₂Se₃, In₂S₃, Bi₂Se₃, Bi₂S₃, ZnSe, ZnS, PbSe, orPbS. In addition, quantum dots formed of these materials can also beused for the photoelectric conversion layer.

Alternatively, the photoelectric conversion layer can have a stackedstructure of a lower semiconductor layer and an upper photoelectricconversion layer. By providing such a lower semiconductor layer, re-bondin the photoelectric conversion layer at the time of charge accumulationcan be prevented, efficiency in transfer of charges accumulated in thephotoelectric conversion layer to the anode or cathode can be increased,and generation of a dark current can be curbed. A material forming theupper photoelectric conversion layer positioned on the light incidenceside may be appropriately selected from the various materials describedabove for forming the photoelectric conversion layer. Meanwhile, as amaterial forming the lower semiconductor layer, it is preferable to usea material having a high value of a band gap (e.g., a value of a bandgap higher than or equal to 3.0 e), and moreover a higher mobility thana material forming the photoelectric conversion layer. Specifically,oxide semiconductor materials such as IGZO; a transition metaldichalcogenide; silicon carbide; diamond; graphene; carbon nanotubes;organic semiconductor materials such as condensed polycyclic hydrocarboncompounds and condensed heterocyclic compounds, and the like can beexemplified. Alternatively, examples of materials forming the lowersemiconductor layer include, in a case in which charge to be accumulatedis electrons, a material having a higher ionization potential than amaterial forming the photoelectric conversion layer, and in a case inwhich charge to be accumulated is holes, a material having lowerelectron affinity than a material forming the photoelectric conversionlayer. Alternatively, it is preferable for the impurity concentration ofa material forming the lower semiconductor layer to be 1×10¹⁸ cm⁻³ orlower. The lower semiconductor layer may have a single layerconfiguration or a multilayer configuration.

In order to improve electrical bondability between the anode-side bufferlayer and the anode or the photoelectric conversion layer, or to adjustthe electric capacity of the imaging element, a first intermediate layermay be provided between the anode and a first buffer layer or the firstbuffer layer and the photoelectric conversion layer. The firstintermediate layer may be provided adjacent to the anode-side bufferlayer (specifically, for example, adjacent to the photoelectricconversion layer side). Examples of a material forming the firstintermediate layer include triarylamine compounds, benzidine compounds,aromatic amine-based materials represented by styrylamine compounds,carbazole derivatives, naphthalene derivatives, anthracene derivatives,phenanthrene derivatives, pyrene derivatives, perylene derivatives,tetracene derivatives, pentacene derivatives, perylene derivatives,picene derivatives, chrysene derivatives, fluoranthene derivatives,phthalocyanine derivatives, subphthalocyanine derivatives,hexaazatriphenylene derivatives, metal complexes having heterocycliccompounds as ligands, thienoacene-based materials represented by thevarious derivatives described above, and compounds includingpoly(3,4-ethylenedioxythiophene)/polystyrene sulfonate [PEDOT/PSS],polyaniline, molybdenum oxide (MoO_(x)), ruthenium oxide (RuO_(x)),vanadium oxide (VO_(x)), and tungsten oxide (WO_(x)). Particularly, forthe purpose of significantly reducing the electric capacity, athienoacene-based material represented by the above-describedderivatives may be preferably used in a case in which a thickness of thefirst intermediate layer is increased.

A cathode-side buffer layer may be formed between the cathode and thephotoelectric conversion layer. Preferred examples of materials to beused for the cathode-side buffer layer include materials having a larger(deeper) work function than a material used for the anode-side bufferlayer, for example, a material which has organic molecules andorganometallic complexes in which a heterocyclic ring containing anitrogen (N) atom is part of a molecular skeleton and further absorbslittle light of the visible light range such as pyridine, quinoline,acridine, indole, imidazole, benzimidazole, and phenanthroline. Inaddition, in a case in which the cathode-side buffer layer is formed ofa thin film having a thickness in the range of about 5×10⁻⁹ m to 2×10⁻⁸m, fullerenes and derivatives thereof represented by C60 and C70 thatabsorb light in the visible light range at a wavelength of 400 nm to 700nm can also be used. In addition, examples of compounds thereof include,specifically, alkali metals such as lithium (Li), sodium (Na), andpotassium (K), halides, oxides, and complex compounds thereof, alkaliearth metals such as magnesium (Mg) and calcium (Ca), and halides,oxides, and complex compounds thereof. However, materials forming thecathode-side buffer layer are not limited to the above. In addition, asecond intermediate layer may be formed between the organicphotoelectric conversion layer and the cathode. Examples of materialsforming the second intermediate layer include aromatic ring-basedcompounds and hydrazone-based compounds. Examples of aromatic ring-basedcompounds include, specifically, monoamine-based compounds andderivatives thereof, alkylene bond-based compounds and derivativesthereof, arylene bond-based compound and derivatives thereof,phenyleneciamine-based compounds and derivatives thereof, andstarburst-based compound and derivatives thereof.

A single-panel color imaging apparatus can be configured using theimaging apparatus according to the first and second aspects of thepresent disclosure. In addition, with the imaging apparatus according tothe first and second aspects of the present disclosure, for example,digital cameras, video camcorders, smartphone cameras, surveillancecameras, and rear-view monitors for automobiles can be configured.

In the imaging apparatus according to the second aspect of the presentdisclosure including the stacked-type imaging element, unlike theimaging apparatus including the Bayer-array imaging element (i.e.,spectroscopy for blue, green, and red is not performed using a colorfilter), a plurality of photoelectric conversion layers havingsensitivity to light of predetermined wavelengths is stacked in thelight incidence direction in the same pixel to form one pixel, and thusimprovement of sensitivity and pixel density per unit volume can beachieve. Furthermore, since an organic material has a high absorptioncoefficient, a film thickness of a photoelectric conversion layer can bethinner as compared to a conventional Si-based photoelectric conversionlayer, and light leakage from adjacent pixels and restriction on thelight incidence angle can be alleviated. Moreover, since theconventional Si-based imaging element produces color signals byperforming interpolation processing among three-color pixels, falsecolor is generated, but false color can be suppressed in the imagingapparatus according to the second aspect of the present disclosureincluding the stacked-type imaging element. Further, since the organicphotoelectric conversion layer itself functions as a color filter, colorseparation can be performed without disposing a color filter.

On the other hand, in the imaging apparatus according to the firstaspect of the present disclosure, due to using a color filler, therequest for spectral characteristics of blue, green and red can bealleviated, and moreover, mass productivity is high. Examples of thearrangement of the imaging element in the imaging apparatus according tothe first aspect of the present disclosure include an interlinearrangement, a G stripe-RB checkered array, a G stripe-RB full-checkeredarray, a checkered complementary color array, a stripe array, a diagonalstripe array, a primary color difference array, a field color differencesequential array, a flame color difference sequential array, an MOS-typearray, a modified MOS-type array, a flame interleave array and a fieldinterleave array in addition to a Bayer array. Here, one pixel (orsubpixel) is formed by one imaging element.

A pixel region in which a plurality of the imaging elements according tothe first to third aspects of the present disclosure or the stacked-typeimaging elements according to an embodiment of the present disclosureare arrayed is formed of a plurality of pixels regularly arranged in atwo-dimensional array. Generally, the pixel region includes an effectivepixel region which actually receives light, amplifies the signal chargesgenerated by photoelectric conversion and reads it out to the drivecircuit, and a black reference pixel region for outputting optical blackserving as a reference of a black level. The black reference pixelregion is generally disposed at the outer peripheral portion of theeffective pixel region.

In the imaging element or the like according to an embodiment of thepresent disclosure including various preferred modes and configurationsdescribed above, light is radiated, photoelectric conversion isgenerated on the photoelectric conversion layer, carriers includingholes and electrons are separated. Further, an electrode from whichholes are extracted is referred to as an anode, and an electrode fromwhich electrons are extracted is defined as a cathode.

In a case in which the stacked-type imaging element is configured, theanode and the cathode can be formed of a transparent conductivematerial. Alternatively, in a case in which the imaging elements or thelike according to an embodiment of the present disclosure are arrangedin a plane, for example, a Bayer array, one electrode of the anode andthe cathode may be formed of a transparent conductive material and theother electrode may be formed of a metal material. In this case,specifically, the cathode positioned on the light incidence side may beformed of a transparent conductive material, and the anode may be formedof, for example, Al—Nd (an alloy of aluminum and neodymium) or Al—Sm—Cu(ASC which is an alloy of aluminum, samarium, and copper) as describedabove. Alternatively, the anode positioned on the light incidence sidemay be formed of a transparent conductive material, and the cathode maybe formed of Al (aluminum), Al—Si—Cu (an alloy of aluminum, silicon, andcopper), or Mg—Ag (an alloy of magnesium and silver).

Further, an electrode formed of a transparent conductive material may bereferred to as a “transparent electrode.” Here, the band gap energy ofthe transparent conductive material is 2.5 eV or more, and preferably,3.1 eV or more. Examples of a transparent conductive material forming antransparent electrode include conductive metal oxides, and specificexamples thereof include indium oxide, indium-tin oxide (ITO includingSn-doped In₂O₃, crystalline ITO and amorphous ITO), indium-zinc oxide(IZO) in which indium is added to zinc oxide as a dopant, indium-galliumoxide (IGO) in which indium is added to gallium oxide as a dopant,indium-gallium-zinc oxide (IGZO, In—GaZnO₄) in which indium and galliumare added to zinc oxide as a dopant, indium-tin-zinc oxide (ITZO) inwhich indium and tin are added to zinc oxide as dopant), IFO (F-dopedIn₂O₃), tin oxide (SnO₂), ATO (Sb-doped SnO₂), FTO (F-doped SnO₂), zincoxide (including ZnO doped with other elements), aluminum-zinc oxide(AZO) in which aluminum is added to zinc oxide as a dopant, gallium-zincoxide (GZO) in which gallium is added to zinc oxide as a dopant,titanium oxide (TiO₂), antimony oxide, spinel type oxide, an oxidehaving a YbFe₂O₄ structure. Alternatively, a transparent electrodehaving a base layer of gallium oxide, titanium oxide, niobium oxide,nickel oxide or the like may be given as an example. The thickness ofthe transparent electrode may be 2×10⁻⁸ m to 2×10⁻⁷ m, preferably 3×10⁻⁸m to 1×10⁻⁷ m.

Alternatively, in a case where transparency is unnecessary, a conductivematerial forming an anode having a function as an electrode forextracting holes is preferably a conductive material having a high workfunction (e.g., φ=4.5 eV to 5.5 eV), and specific examples thereofinclude gold (Au), silver (Ag), chromium (Cr), nickel (Ni), palladium(Pd), platinum (Pt), iron (Fe), iridium (Ir), germanium (Ge), osmium(Os), rhenium (Re), tellurium (Te), or alloys thereof. On the otherhand, a conductive material forming an cathode having a function as anelectrode for extracting electrons is preferably a conductive materialhaving a low work function (e.g., φ=3.5 eV to 4.5 eV), and specificexamples thereof include alkali metals (e.g., Li, Na, K, etc.) and thefluorides or oxides thereof, alkaline earth metals (e.g., Mg, Ca, etc.)and the fluorides or oxides thereof, aluminum (Al), zinc (Zn), tin (Sn),thallium (Tl), a sodium-potassium alloy, an aluminum-lithium alloy, amagnesium-silver alloy, indium and rare earth metals such as ytterbium.Alternatively, examples of the material forming an anode or cathodeinclude metals such as platinum (Pt), gold (Au), palladium (Pd),chromium (Cr), nickel (Ni), aluminum (Al), silver (Ag), tantalum (Ta),tungsten (W), copper (Cu), titanium (Ti), indium (In), tin (Sn), iron(Fe), cobalt (Co), molybdenum (Mn) or the like, or alloys includingthese metal elements, as conductive particles formed of these metals,conductive particles of alloys containing these metals, polysiliconcontaining impurities, carbon-based materials, oxide semiconductorsmaterials, conductive materials such carbon nanotubes, graphene and thelike, and a laminated structure of layers containing these elements.Furthermore, examples of the material forming an anode or cathodeinclude organic materials (conductive polymers) such as poly(3,4-ethylenedioxythiophene)/polystyrenesulfonate [PEDOT/PSS]. Further,a paste or ink prepared by mixing these conductive materials into abinder (polymer) may be cured to be used as an electrode.

A dry method or wet method may be used as a film-forming method of ananode and a cathode. Examples of the dry method include a physical vapordeposition method (PVD method) and a chemical vapor deposition method(CVD) method. Examples of the film-forming method using the principle ofPVD method include a vacuum evaporation method using resistance heatingor high frequency heating, an electron beam (EB) evaporation method,various sputtering methods (magnetron sputtering method, RF-DC coupledbias sputtering method, ECR sputtering method, facing-target sputteringmethod and high frequency sputtering method), an ion plating method, alaser ablation method, a molecular beam epitaxy method, and a lasertransfer method. Furthermore, examples of the CVD method include aplasma CVD method, a thermal CVD method, an organometallic (MO) CVDmethod, and a photo CVD method. On the other hand, examples of the wetmethod include an electrolytic plating method and an electroless platingmethod, a spin coating method, an ink jet method, a spray coatingmethod, a stamping method, a micro contact printing method, aflexographic printing method, an offset printing method, a gravureprinting method, a dipping method, etc. As for patterning, chemicaletching such as shadow mask, laser transfer, photolithography and thelike, physical etching by ultraviolet light, laser and the like may beused. A planarization is treated to the anode and a cathode ifnecessary, examples of a planarization technique include a laserplanarization method, a reflow method, a chemical mechanical polishing(CMP) method, etc.

A dry film formation method and a wet film formation method may be givenas examples of a film-forming method for various organic layers. VariousPVD methods may be given as examples of the dry film formation method,and specifically the methods include a vacuum deposition method usingresistance heating, high frequency or electron beam heating, a flashdeposition method, a plasma deposition method, an EB deposition method,various sputtering method (bipolar sputtering method, direct currentsputtering method, DC magnetron sputtering method, RF-DC coupled biassputter method, ECR sputtering method, facing-target sputtering method,high frequency sputtering method and ion beam sputtering method), a DC(direct current) method, an RF method, a multi-cathode method, anactivation reaction method, an electric field vapor deposition method, ahigh frequency ion plating method and a reactive ion plating method, alaser ablation method, a molecular beam epitaxy method, a laser transfermethod, and a molecular beam epitaxy (MBE) method. Alternatively, in acase in which imaging elements for forming an imaging apparatus areintegrated, a method of forming a pattern on the basis of a PLD method(pulsed laser deposition method) may also be employed. Furthermore,examples of a chemical vapor deposition (CVD) method include a plasmaCVD method, a thermal CVD method, an MOCVD method, and a photo CVDmethod. On the other hand, as a wet method, a spin coating method; adipping method; casting method; a micro contact printing method; a dropcasting method; various printing methods such as a screen printingmethod, an ink jet printing method, an offset printing method, a gravureprinting method and a flexographic printing method; a stamping method; aspray coating method; various coating methods such as an air doctorcoater method, a blade coater method, a rod coater method, a knifecoater method, a squeeze coater method, a reverse roll coater method, atransfer roll corner method, a gravure coater method, a kiss coatermethod, a cast coater method, a spray coater method, a slit orificecorner method and a calendar coater method. Further, examples of asolvent in the coating method include a nonpolar or low polar organicsolvents such as toluene, chloroform, hexane, and ethanol, however, thesolvent is not limited thereto. As for patterning, chemical etching suchas shadow mask, laser transfer, photolithography and the like, physicaletching by ultraviolet light, laser and the like may be used. Examplesof a planarization technique for various organic layers include a laserplanarization method, a reflow method, etc. Further, in order to copewith miniaturization of one layer of the imaging elements, it ispreferable to employ a dry film forming method (specifically, PVDmethod) as a film forming method for the organic layers and theanode-side buffer layer.

The imaging elements according to the first to third aspects of thepresent disclosure can be formed on a substrate in some cases. Here,examples of the substrate include organic polymers exemplified bypolymethyl methacrylate (polymethylmethacrylate or PMMA), polyvinylalcohol (PVA), polyvinyl phenol (PVP), polyethersulfone (PES),polyimide, polycarbonate (PC), polyethylene terephthalate (PET), orpolyethylene naphthalate (PEN) (having a form of a polymeric materialsuch as a plastic film, a plastic sheet, or a plastic substrate formedof a polymeric material having flexibility), or mica. If a substrateformed of such a polymeric material having flexibility is used, forexample, incorporation or integration of an electronic device with animaging element or the like having a curved surface shape is possible.Alternatively, examples of the substrate include various glasssubstrates, various glass substrates with an insulating film formed ontheir surfaces, quartz substrates, quartz substrates with an insulatingfilm formed on their surfaces, silicon semiconductor substrates, siliconsemiconductor substrates with an insulating film formed on theirsurfaces, various alloys such as stainless steel, and metal substratesformed of various metals. In addition, examples of an insulating filminclude a silicon oxide-based material (e.g., SiO_(X) or spin-on-glass(SOG)); silicon nitride (SiN_(Y)); silica oxynitride (SiON); aluminumoxide (Al₂O₃); a metal oxide or a metal salt. In addition, an organicinsulating film can be formed, and examples of materials thereofinclude, for example, lithography-enabled polyphenol-based materials,polyvinylphenol-based materials, polyimide-based materials,polyamide-based materials, polyamide imide-based materials, fluorinatedpolymer materials, borazine-silicon polymer materials, truxene-basedmaterials, and the like. Alternatively, a conductive substrate with suchan insulating film formed on a surface (a substrate formed of a metalsuch as gold or aluminum, or a substrate formed of highly-orientedgraphite) may also be used. Although it is desirable for the surface ofthe substrate to be smooth, it does not matter if it has roughness tothe extent that it does not adversely affect characteristics of thephotoelectric conversion layer. By forming a silanol derivative on thesurface of the substrate using a silane coupling method, forming a thinfilm formed of a thiol derivative, a carboxylic acid derivative, aphosphoric acid derivative, or the like thereon using an SAM method orthe like, or forming a thin film formed of an insulating metal salt ormetal complex using a CVD method or the like, adhesion between theelectrode and the substrate may be improved. In addition, the electrodescan be treated using oxygen plasma, argon plasma, nitrogen plasma,ozone, or the like. This treatment can be performed regardless ofwhether there is an electrode coating layer or before and after coating.A transparent substrate is a substrate formed of a material that doesnot excessively absorb light incident on the photoelectric conversionlayer though the substrate.

The electrodes and the photoelectric conversion layer may be covered bya coating layer in some cases. Examples of materials forming the coatinglayer include inorganic insulating materials exemplified by siliconoxide-based materials; silicon nitride (SiN_(Y)); a metal oxidehigh-dielectric constant insulating film such as aluminum oxide (Al₂O₃)or the like as well as organic insulating materials (organic polymers)exemplified by polymethyl methacrylate (PMMA); polyvinyl phenol (PVP);polyvinyl alcohol (PV_(A)); polyimide, polycarbonate (PC); polyethyleneterephthalate (PET); polystyrene; silanol derivatives (silane couplingagents) such as N-2 (aminoethyl) 3-aminopropyltrimethoxysilane(AEAPTMS), 3-mercaptopropyltrimethoxysilane (MPTMS),octadecyltrichlorosilane (OTS) or the like; straight-chain hydrocarbonshaving a functional group capable of bonding to the electrode at one endsuch as octadecanethiol, dodecyl isocyanate and the like, andcombinations thereof. In addition, examples of the silicon oxide-basedmaterials include silicon oxide (SiO_(X)), BPSG, PSG, BSG, AsSG, PbSG,silicon oxynitride (SiON), spin-on-glass (SOG), and low dielectricconstant materials (e.g., polyaryl ether, cycloperfluorocarbon polymersand benzocyclobutene, cyclic fluoro resins, polytetrafluoroethylene,fluoroaryl ether, fluorinated polyimide, amorphous carbon and organicSOG). Examples of insulating layer forming methods include, for example,the above-described dry film forming method and wet film forming method.

A photoelectric conversion element can be formed of the imaging elementof the present disclosure, optical sensors, image sensors, rear-viewmonitors for automobiles, and solar cells in addition to imagingapparatuses (solid-state imaging apparatuses) such as television camerascan be formed using such photoelectric conversion elements.

An on-chip micro lens and a light shielding layer may be provided in theimaging element or the imaging apparatus if necessary. A shutter forcontrolling incidence of light on the imaging element may be installedif necessary, or an optical cut filter may be included in accordancewith a purpose of the imaging apparatus. A drive circuit for drivingimaging elements and wiring may be provided in the imaging apparatus.

The configuration and structure of the floating diffusion layer, theamplification transistor, reset transistor and select transistor formingthe control unit may be the same as the conventional floating diffusionlayer, amplification transistor, reset transistor and select transistor.Also, the drive circuit may have well-known configuration and structure.

Either one of an anode and a cathode is connected to the floatingdiffusion layer and the gate section of the amplification transistor,and a contact hole portion may be formed to connect the electrode to thefloating diffusion layer and the gate section of the amplificationtransistor. Examples of a material forming the contact hole portioninclude a high melting point metal such as tungsten, Ti, Pt, Pd, Cu,TiW, TiN, TiNW, WSi₂, MoSi₂ or the like, metal silicide, or a stackedstructure of layers formed of these materials (e.g., Ti/TiN/W).

For example, in a case where the imaging apparatus is stacked with areadout integrated circuit (ROIC), the stacking may be performed byoverlaying a drive substrate on which a readout integrated circuit and aconnection portion formed of copper (Cu) are formed and an imagingelement on which a connection portion is formed such that the connectionportions are in contact with each other, and joining the connectionportions, and it is also possible to join the connection portions usinga solder bump or the like.

Embodiment 1

Embodiment 1 relates to the imaging element according to first to thirdaspects of the present disclosure and the imaging apparatus according tothe first aspect of the present disclosure.

As conceptual diagrams are illustrated in FIG. 1A, FIG. 1B, FIG. 2A, andFIG. 2B, an imaging element (photoelectric conversion element) 11 ofEmbodiment 1 has at least an anode 21, an anode-side buffer layer 22, aphotoelectric conversion layer 23, and a cathode 25 sequentiallystacked. Specifically, the imaging element 11 of Embodiment 1 has theanode 21, the anode-side buffer layer 22, the organic photoelectricconversion layer 23, a cathode-side buffer layer 24, and the cathode 25stacked in order. In addition, the anode-side buffer layer 22 includes amaterial having the above-described structural formula (1), structuralformula (2), or structural formula (3) in which thiophene and carbazoleare combined. More specifically, in Embodiment 1, the anode-side bufferlayer 22 is formed of a material having the following structural formula(4) [compound (A)] or a material having the following structural formula(5) [compound (B)] in which thiophene and carbazole are combined. In theimaging elements illustrated in FIG. 1A and FIG. 2B, light is incidentfrom the cathode side. On the other hand, in the imaging elementsillustrated in FIG. 1B and FIG. 2A, light is incident from the anodeside. Light may also be incident from a substrate 20 side. Further, aflow of holes (indicated by “+” in circles) and electrons (indicated by“−” in circles) generated from photoelectric conversion is schematicallyillustrated in FIG. 3B.

An imaging apparatus 40 of Embodiment 1 may have a plurality of imagingelements 11 of Embodiment 1. Specifically, blue imaging elements, greenimaging elements, and red imaging elements are arranged in a plane likea Bayer array.

Materials forming the organic photoelectric conversion layer are asdescribed above, or may be as follows.

That is, examples of materials for the organic photoelectric conversionlayer 23 included in a blue imaging element having the organicphotoelectric conversion layer that is sensitive to blue and absorbsblue light (light having a wavelength of 425 nm to 495 nm) include, inaddition to quinacridone or quinacridone derivatives, andthienoacen-based materials represented by the above-described variousderivatives, naphthalene derivatives, anthracene derivatives,phenanthrene derivatives, pyrene derivatives, tetracene derivatives,picene derivatives, chrysene derivatives, fluoranthene derivatives,metal complex and the like as p-type organic semiconductor materials,and fullerene and fullerene derivatives, and organic semiconductormaterials having a higher (deeper) HOMO value and LUMO value than thoseof p-type organic semiconductor materials as n-type organicsemiconductor materials. More specifically, two or more types ofmaterials are extracted from organic light absorbing materials ororganic transparent materials (examples of the organic light absorbingmaterials or organic transparent materials include aromatic monocycliccompounds, aromatic condensed cyclic compounds, hetero monocycliccompounds, condensed heterocycle compounds, polymethine compounds,π-conjugated low molecular compounds, carbonium compounds, styryl-basedcompounds, stilbene-based compounds, metal complex-based compounds,π-conjugated high molecular compounds, σ-conjugated compounds,pigment-containing polymeric compounds, and polymer complex-basedcompounds), materials having a small (shallow) HOMO and LUMO values maybe for p-type organic semiconductors, and materials having a large(deep) HOMO and LUMO values may be for n-type organic semiconductors,and a combination of two or more types of materials in which any onetype absorbs blue light may be exemplified. Although a thickness of theorganic photoelectric conversion layer is not limited, for example,values of 1×10⁻⁸ m to 5×10⁻⁷ m, preferably 2.5×10⁻⁸ m to 3×10⁻⁷ m, morepreferably 2.5×10⁻⁸ m to 2×10⁻⁷ m, and even more preferably 1×10⁻⁷ m to2.5×10⁻⁷ m may be exemplified.

Examples of materials for the organic photoelectric conversion layer 23included in a green imaging element having the organic photoelectricconversion layer that is sensitive to green and absorbs green light(light having a wavelength of 495 nm to 570 nm) include, in additionquinacridone or quinacridone derivatives, and thienoacen-based materialsrepresented by the above-described various derivatives, anthracenederivatives, phenanthrene derivatives, pyrene derivatives, perylenederivatives, tetracene derivatives, fluoranthene derivatives,subphthalocyanine derivatives, and metal complexes having heterocycliccompounds as ligands p-type organic semiconductor materials, andfullerene and fullerene derivatives, organic semiconductor materialshaving larger (deeper) HOMO and LUMO values than those of p-type organicsemiconductors, transparent inorganic metal oxide as n-type organicsemiconductor materials. Examples of n-type organic semiconductormaterials include, specifically, heterocyclic compounds containingnitrogen atoms, oxygen atoms, and sulfur atoms, for example, organicmolecules having pyridine, pyrazine, pyrimidine, triazine, quinoline,quinoxaline, isoquinoline, acridine, phenadine, phenanthroline,tetrazole, pyrazole, imidazole, thiazole, oxazole, imidazole,benzimidazole, benzotriazole, benzoxazole, benzoxazole, carbazole,benzofuran, dibenzofuran and the like in a part of the molecularskeleton, organometallic complexes, and subphthalocyanine derivatives.More specifically, two or more types of materials are extracted fromorganic light absorbing materials or organic transparent materials(examples of the organic light absorbing materials or organictransparent materials include aromatic monocyclic compounds, aromaticcondensed cyclic compounds, hetero monocyclic compounds, condensedheterocycle compounds, polymethine compounds, π-conjugated low molecularcompounds, carbonium compounds, styryl-based compounds, stilbene-basedcompounds, metal complex-based compounds, π-conjugated high molecularcompounds, σ-conjugated compounds, pigment-containing polymericcompounds, and polymer complex-based compounds), materials having asmall (shallow) HOMO and LUMO values may be for p-type organicsemiconductor materials, and materials having a large (deep) HOMO andLUMO values may be for n-type organic semiconductor materials, and acombination of two or more types of materials in which any one typeabsorbs green light may be exemplified. Although a thickness of theorganic photoelectric conversion layer is not limited, for example,values of 1×10⁻⁸ m to 5×10⁻⁷ m, preferably 2.5×10⁻⁸ m to 3×10⁻⁷ m, morepreferably 2.5×10⁻⁸ m to 2.5×10⁻⁷ m, and even more preferably 1×10⁻⁷ mto 2.5×10⁻⁷ m may be exemplified.

Examples of materials for the organic photoelectric conversion layer 23included in a red imaging element having the organic photoelectricconversion layer that is sensitive to red and absorbs red light (lighthaving a wavelength of 620 nm to 750 nm) include, in addition toquinacridone or quinacridone derivatives, and thienoacen-based materialsrepresented by the above-described various derivatives, pentacenederivatives, perylene derivatives, fluoranthene derivatives,phthalocyanine derivatives, subphthalocyanine derivatives, mid metalcomplexes having heterocyclic compounds as ligands as p-type organicsemiconductor materials, and fullerene and fullerene derivatives,organic semiconductor materials having larger (deeper) HOMO and LUMOvalues than those of p-type organic semiconductors, transparentinorganic metal oxide as n-type organic semiconductor materials.Examples of n-type organic semiconductor materials include,specifically, heterocyclic compounds containing nitrogen atoms, oxygenatoms, and sulfur atoms, for example, organic molecules having pyridine,pyrazine, pyrimidine, triazine, quinoline, quinoxaline, isoquinoline,acridine, phenadine, phenanthroline, tetrazole, pyrazole, imidazole,thiazole, oxazole, imidazole, benzimidazole, benzotriazole, benzoxazole,benzoxazole, carbazole, benzofuran, dibenzofuran and the like in a partof the molecular skeleton, organometallic complexes andsubphthalocyanine derivatives. More specifically, two or more types ofmaterials are extracted from organic light absorbing materials ororganic transparent materials (examples of the organic light absorbingmaterials or organic transparent materials include aromatic monocycliccompounds, aromatic condensed cyclic compounds, hetero monocycliccompounds, condensed heterocycle compounds, polymethine compounds,π-conjugated low molecular compounds, carbonium compounds, styryl-basedcompounds, stilbene-based compounds, metal complex-based compounds,π-conjugated high molecular compounds, σ-conjugated compounds,pigment-containing polymeric compounds, and polymer complex-basedcompounds), materials having a small (shallow) HOMO and LUMO values maybe for p-type organic semiconductors, and materials having a large(deep) HOMO and LUMO values may be for n-type organic semiconductors,and a combination of two or more types of materials in which any onetype absorbs red light may be exemplified. Although a thickness of theorganic photoelectric conversion layer is not limited, for example,values of 1×10⁻⁸ m to 5×10⁻⁷ m, preferably 2.5×10⁻⁸ m to 3×10⁻⁷ m, morepreferably 2.5×10⁻⁸ m to 2.5×10⁻⁷ m, and even more preferably 1×10⁻⁷ mto 2.5×10⁻⁷ m may be exemplified.

In the imaging element of Embodiment 1, one of the anode 21 and thecathode 25 is formed of a transparent conductive material and the otheris formed of a metal material. Here, since light is incident from thecathode on the imaging elements illustrated in FIG. 1 and FIG. 2B, thecathode 25 may be formed of a transparent conductive material (e.g.,ITO), and the anode 21 may be formed of Al—Nd (an alloy of aluminum andneodymium) or ASC (an alloy of aluminum, samarium, and copper). On theother hand, since light is incident from the anode side on the imagingelement illustrated in FIG. 1B and FIG. 2A, the anode 21 may be formedof a transparent conductive material (e.g., ITO), and the cathode 25 maybe formed of Al (aluminum), Al—Si—Cu (an alloy of aluminum, silicon, andcopper), or Mg—Ag (an alloy of magnesium and silver).

A material expressed by the above-described structural formula (4)[compound (A)] forming the anode-side buffer layer was synthesized onthe basis of the synthetic scheme having four steps as illustrated inFIG. 14.

[First Step]

(1) 50.6 grams of (156 millimoles, 1.00 molar equivalent)3,6-dibromocarbazole, 500 milliliters of THF, and 46.5 grams (213millimoles, 1.37 molar equivalent) of (Bo)₂O were prepared in anargon-replaced one-liter four-necked flask. Further, “Bo” means atert-butoxycarbonyl group.

(2) 2.30 grams (18.8 millimoles, 0.12 molar equivalent) ofN,N-dimethyl-4-aminopyridine (DMAP) were added thereto little by little.

(3) The mixture was stirred at room temperature for 2 hours.

(4) The reaction solution was poured into 1.5 liters of water andprecipitated crystal was filtered.

(5) The obtained crystal was dissolved into 1.5 liters of chloroformthen dried using magnesium sulfate and filtered.

(6) 200 milliliters of ethanol was added to the filtrate and it wasconcentrated under reduced pressure to be 300 milliliters.

(7) The crystal precipitated in the concentrate was filtered.

(8) The filtrate was suspended in 1 liter of isopropyl alcohol, washed,and filtered.

(9) The obtained while crystal was dried at 80° C. for 2 hours underreduced pressure, and thereby 63.7 grams (150 millimoles at a yield of96.3%) of intermediate 1-1 was obtained. The purity was analyzed by HPLCand found to be 99.7%. As a result of structural analysis by ¹H NMR, thedesired number of protons was obtained and it was possible to identifythat it was the intermediate 1-1.

[Second and Third Steps]

Since some protection groups are deprotected when an intermediate 1-2 issynthesized, the third step was continuously performed together andidentification was performed after purification. The synthesis order isas follows.

(1) 57.0 grams (134 millimoles, 1 molar equivalent) of the intermediate1-1, 47.7 grams (282 millimoles, 2.10 molar equivalent) ofdiphenylamine, 2 liters of deoxygenated xylene, and 38.7 grams (402millimoles, 3.00 molar equivalent) of NaOtBu were prepared in anargon-replaced four-liter four-necked flask.

(2) Bubbling was performed thereon using argon gas for 30 minutes.

(3) 20.0 milliliters (6.70 millimoles, 0.05 molar equivalent) of 10%P(tBu)₃ hexane solution and 2.85 grams (4.96 millimoles, 0.04 molarequivalent) of Pd(dBa)₂ were added thereto.

(4) The temperature was increased to 107° C. and the mixture was stirredfor one hour.

(5) After cooling, the reaction solution was added to 500 milliliters ofwater and separated.

(6) The water layer obtained in (5) was extracted twice using 500milliliters of toluene.

(7) The organic layers obtained in (5) and (6) were combined and driedusing magnesium sulfate.

(8) After filtration, the filtered solution was concentrated underreduced pressure to be about 1.5 liters.

(9) 131 milliliters (1.70 millimoles, 12.7 molar equivalent) oftrifluoroacetic acid were added to the concentrated solution and it wasstirred at 90° C. for one hour.

(10) After cooling, the reaction solution was poured into a sodiumcarbonate aqueous solution to make it alkaline and separated.

(11) After the organic layer was cleansed using water, it was driedusing magnesium sulfate and filtered.

(12) The filtrate was filtered through Florisil filtration (Florisil:500 grams with toluene as a solvent).

(13) The filtrate was concentrated to dryness.

(14) Chloroform was added to the residue to be dissolved, and 500milliliters of methanol were added thereto.

(15) The mixture was concentrated under reduced pressure to be about 500milliliters, and precipitated crystal was filtered.

(16) 38.4 grams (76.6 millimoles at a yield of 57.1%) of an intermediate1-3 of brown crystal coarse bodies could be obtained.

(17) The crystal obtained in (16) was dispersed in 300 milliliters oftoluene and refluxed for one hour.

(18) The mixture was cooled up to 40° C. and then filtered.

(19) The obtained crystal was dried at 60° C. under reduced pressure fortwo hours, and thereby 25.1 grams (50.0 millimoles at an overall yieldof 37.3% from the second step to the third step) of a light yellowcrystal compound 1-3 were obtained. The intermediate 1-3 could beidentified through structural analysis by ¹H NMR and MALDI-TOF-MS.

[Fourth Step]

(1) 6.16 grams (19.0 millimoles, 1.00 molar equivalent) of5,5′-dibromo-2,2′-bithiophene, 20.0 grams (399.9 millimoles, 2.10 molarequivalent) of the intermediate 1-3, 31.4 grams (148 millimoles, 7.79molar equivalent) of tripotassium phosphate, and 120 milliliters ofdehydrated 1,4-dioxane were prepared in an argon-replaced Schlenk tube.

(2) Bubbling was performed thereon using argon gas for 30 minutes.

(3) 0.70 milliliters (5.84 millimoles, 0.31 molar equivalent) oftrans-1,2-cyclohexanediamine and 745 milligrams (3.91 millimoles 0.21molar equivalent) of CuI were added thereto.

(4) The mixture was stirred overnight with heating under reflux.

(5) Since an intermediate remained, 0.50 milliliters (4.17 millimoles,0.22 molar equivalent) of trans-1,2-cyclohexanediamine and 378milligrams (1.98 millimoles, 0.10 molar equivalent) of CuI were addedthereto.

(6) The mixture was stirred overnight with heating under reflux.

(7) Since an intermediate remained in a very small amount, 0.50milliliters (4.17 millimoles, 0.22 molar equivalent) oftrans-1,2-cyclohexanediamine and 130 milligrams (0.68 millimoles, 0.04molar equivalent) of CuI were added thereto and refluxed, but the changewas small, and thus heating was finished.

(8) After cooling, the reaction solution was poured in to water.

(9) Since an oily substance and a solid were mixed, ultrasonic waveswere applied thereto for 15 minutes to disperse crystals and they werefiltered.

(10) The obtained crystal was taken out and suspended and cleansed in200 milliliters of acetonitrile, and then filtered.

(11) 40.5 grams of the obtained brown crystal were dried at 80° C. underreduced pressure for one hour.

(12) 23.6 grams of crystal were dissolved in toluene and filtered usingactivated clay (100 grams) and silica gel (200 grams of PSQ).

(13) The yellow filtrate was concentrated under reduced pressure to beabout 50 milliliters, heptane was added thereto, and the precipitatedcrystal was filtered.

(14) After the crystal was dried and/or reduced pressure, 16.3 grams(14.0 millimoles) of the compound (A) which is yellow crystal wereobtained.

(15) Soxhlet extraction was performed on the coarse bodies of thecompound (A) obtained in (14) twice to purify them.

(16) The compound was dried at 80° C. under reduced pressure for onehour, and thereby 7.70 grams (6.61 millimoles at an extraction yield of79.1%) of the Compound (A) were obtained. As a result of purity analysisusing HPLC after that, the purity of 97.1% was confirmed.

Sublimation purification was performed on the compound (A) that hadundergone Soxhlet extraction twice. Specifically, the followingoperations were performed.

(1) 2.00 grams of the compound (A) was prepared in the raw material partof a sublimation purification device.

(2) After pressure inside the sublimation tube was reduced to 7.2×10⁻⁴Pa, sublimation purification was performed.

(3) After sublimation was finished, the compound (A) precipitated in thecollection tube was recovered. The recovered amount was 1.29 grams(sublimation recovery rate of 64.3%).

(4) Purity analysis was performed on the compound (A) that had undergonesublimation purification using HPLC, the purity of 99.1% was confirmed.In addition, the substance was identified as the compound (A) throughstructural analysis by ¹H NMR and mass spectrometry using MALDI-TOF-MS.The analysis result of ¹H NMR is shown in FIG. 15 and the analysisresult of MALDI-TOF-MS is shown in FIG. 16.

The material [compound (B)] having the above-described structuralformula (5) was obtained on the basis of the same synthesis scheme asthat of the compound (A) illustrated in FIG. 14, however, by usingp,p′-ditolylamine in place of diphenylamine as the compound reacted tothe intermediate 1-1 in (1) of the second step.

An imaging element for evaluation was produced in the following methodas indicated in the schematic partial sectional view of FIG. 3A.Further, the imaging element for evaluation was set as a green imagingelement.

An ITO film having a thickness of 120 nm was formed on the substrate 20formed of a quartz substrate using a sputtering device, and the anode 21formed of the ITO film was formed using a photolithography and etchingtechniques. Next, the insulating layer 31 was formed on the substrate 20and the anode 21, then the insulating layer 31 was patterned using thephotolithography and etching techniques, the anode 21 in a size of 1 mmsquare was exposed, and then ultrasonic cleansing was performed thereonusing a detergent, acetone, and ethanol. Then, after the substrate wasdried, UV/ozone treatment was further performed thereon for 10 minutes.Next, the substrate 20 was fixed to a substrate holder of a vacuumdeposition device, and pressure of the deposition tank was reduced to5.5×10⁻⁵ Pa.

After that, the anode-side buffer layer having a thickness of 10 nmformed of a material having the above-described structural formula (4)or structural formula (5) was formed on the basis of the vacuumdeposition method using a shadow mask. Next, 2Ph-BTBT which is a p-typesemiconductor material expressed in the following structural formula(11), fluorinated subphthalocyanine chloride (F6-SubPc-Cl) thatfunctions as a pigment material expressed in the following structuralformula (12), and C60 which is an n-type semiconductor material as shownbelow were co-deposited on the anode-side buffer layer at a depositionspeed ratio of 4:4:2 to have a thickness of 230 nm, and thephotoelectric conversion layer 23 formed of a mixed layer of the p-typeorganic semiconductor material and the n-type organic semiconductormaterial (bulk heterostructure) was obtained. Continuously, B4PyMPM (seethe following structural formula (13)) was deposited to be 5 nm, andthereby the cathode-side buffer layer 24 was obtained. After that, itwas put into a container with an inert gas atmosphere and loaded into asputtering device, a film of ITO was formed on the cathode-side bufferlayer 24 to have a thickness of 50 nm, and thereby the cathode 25 wasobtained. After that, processes in a case in which an actual imagingelement and imaging apparatus were formed, particularly, formation ofcolor filters, formation of a protective film, and thermal treatmentassuming a heating process such as soldering for the imaging element at150° C. for 2.5 hours were performed in a nitrogen atmosphere, andthereby an imaging element for evaluation of Embodiment 1A asillustrated in the schematic partial sectional views of FIG. 3A and FIG.1A was obtained. Alternatively, after the cathode-side buffer layer 24was formed, the cathode 25 formed of an aluminum (Al) layer having athickness of 100 nm was obtained in the same vacuum deposition device.After that, processes in the case in which an actual imaging element andimaging apparatus were formed, particularly, formation of color filters,formation of a protective film, and thermal treatment assuming a heatingprocess such as soldering for the imaging element at 150° C. for 2.5hours were performed in a nitrogen atmosphere, and thereby an imagingelement for evaluation of Embodiment 1B as illustrated in the schematicpartial sectional views of FIG. 3A and FIG. 2A was obtained.

Physical property value evaluation was performed on the material used inthe anode-side buffer layer on the basis of the method described below.

That is, in measurement of a HOMO (ionization potential) value, each offilms of the compound (A), the compound (B), a compound (C) expressed bythe following structural formula (21), and a compound (D) expressed bythe following structural formula (22) was formed on an Si substrate tohave a thickness of 20 nm, the thin film surfaces thereof were measuredusing UV photoelectron spectroscopy (UPS), and thereby the HOMO valuewas obtained. In addition, the optical energy gap was calculated fromthe absorption edge of the absorption spectrum of the thin film of eachmaterial, and the LUMO value was calculated from the difference betweenthe HOMO value and the energy gap. Here, the value can be expressed asfollows.LUMO=−|(HOMO)−(energy gap)|

With respect to mobility, an element for hole mobility measurement wasproduced using the following method and evaluated. First, a Pt thin filmhaving a thickness of 100 nm was formed using an EB deposition method,and an anode formed of Pt was formed on the basis of the lithographytechnique using a photomask. Next, an insulating layer was formed on asubstrate and the anode, the anode in a size of 0.25 mm square wasexposed using the lithography technique, and a film of molybdenum oxide(MoO₃) having a thickness of 1 nm, a thin film formed of the compound(A), the compound (B), the compound (C), and the compound (D) having athickness of 200 nm for measuring hole mobility, a film of molybdenumoxide (MoO₃) having a thickness of 3 nm, and a cathode formed of Auhaving a thickness of 100 nm were formed thereon using a depositionmethod. Then, voltage from −1 V to −20 V or +1 V to +20 V were appliedto the element for mobility film formation obtained as described above,a formula of a space charge limited current (SCLC) was fitted to acurrent-voltage curve by which a current flowed by the negative bias orpositive bias, and hole mobility at −1 V or +1 V was measured. The HOMOvalues, LUMO values, and mobility of the compound (A), compound (B),compound (C), and compound (D) measured as described above are shown inTables 1 and 2. In addition, the compound (A) was deposited to form afilm on a quartz substrate to thickness of 50 nm, and the absorptionspectrum in a case in which the thickness is converted to the thicknessof 10 nm is shown in FIG. 17. In a case in which an absorption maximumof the compound (A) appears at a wavelength of 400 nm or lower and isused in the anode-side buffer layer, the compound absorbs a small amountof visible light and has spectral characteristics of not disturbingphotoelectric conversion of incident light on a layer positioned on thecathode side rather than the anode-side buffer layer. In addition,spectral characteristics of the compound (A) are favorable in comparisonto general organic semiconductor materials.

Evaluation of the imaging element was performed on the basis of themethod described below.

That is, the imaging element was placed on a prober stage of which thetemperature was controlled at 60° C., while a voltage of −2.6 V(so-called reverse-biased voltage 2.6 V) was applied between the cathodeand the anode, light irradiation was performed under conditions of awavelength of 560 nm and 2 μW/cm², and thereby the light current wasmeasured. After that, the light irradiation was stopped and the darkcurrent was measured. Next, an external quantum efficiency EQE wasobtained from the light current and dark current using the followingformula. Further, “1240” is a constant, and “560” is the wavelength ofthe irradiated light.EQE=|((light current−dark current)×100/(2×10⁻⁶))×(1240/560)×100|)

In addition, in evaluation for afterimages, while a voltage of −2.6 Vwas applied between the cathode and the anode, light irradiation wasperformed under conditions of a wavelength of 560 nm and 2 μW/cm², thenwhen the light irradiation was stopped, T₀ when the amount of currentflowing between the cathode and the anode immediately before the stop ofthe light irradiation was set to I₀ and the time taken until the amountof current became (0.03×I₀) after the stop of the light irradiation wasset to T₀, was set as an afterimage time. Table 1 shows values ofexternal quantum efficiency, dark current, and afterimage time of thecompound (A) and compound (B) relative to those of the compound (C), andTable 2 shows values of external quantum efficiency, dark current, andafterimage time of the compound (A) relative to those of the compound(D). Further, samples according to the above-described Embodiment 1A andEmbodiment 1B were produced on the basis of the compound (A). Inaddition, samples having the same structure as that of Embodiment 1Awere produced on the basis of the compound (B) and compound (C), and asample having the same structure as that of the above-describedEmbodiment 1B was produced on the basis of the compound (D).

TABLE 1 Compounds (A) (B) (C) HOMO eV −5.4 −5.4 −5.4 LUMO eV −2.5 −2.6−2.1 Hole mobility ×10⁻⁵ cm²/V/s 3.7 5.0 0.55 External quantum Relativevalue 1.04 1.05 1.00 efficiency Dark current Relative value 0.53 0.521.00 Afterimage time Relative value 0.11 0.10 1.00

TABLE 2 Compounds (A) (D) HOMO eV −5.4 −5.5 LUMO eV −2.5 −2.4 Holemobility ×10⁻⁵ cm²/V/s 3.7 0.011 External quantum Relative value 1.021.00 efficiency Dark current Relative value 0.73 1.00 Afterimage timeRelative value 0.15 1.00

As is apparent from Table 1, the external quantum efficiency was 4% to5% higher, the dark current could be curbed by about half, and theafterimage time could be significantly improved to about 1/10 when thecompound (A) or compound (B) was used than when the compound (C) used asthe anode-side buffer layer. In addition, as is apparent from Table 2,the external quantum efficiency was 2% higher, the dark current could becurbed to about 70%, and the afterimage time could be significantlyimproved to 15% when the compound (A) was used than when the compound(D) was used as the anode-side buffer layer.

However, the above-described patent publication describes that, bysatisfying the condition that electron affinity of the electron blockinglayer is smaller 1.3 eV or more than the work function of an adjacentelectrode and the ionization potential of the electron blocking layer isequivalent to or smaller than the ionization potential of an adjacentphotoelectric conversion layer, an organic photoelectric conversionelement in which photoelectric conversion efficiency does not decreasewithout an increase of a dark current even if a voltage is applied fromoutside can be provided.

Here, since the work function of the anode of Embodiment 1 is −4.8 eVand the LUMO values of the compound (A), compound (B), compound (C), andcompound (D) are −2.5 eV, −2.6 eV, −2.1 eV, and −2.4 eV respectively,the condition that the LUMO value is smaller by 1.3 eV or more than thework function of the anode is satisfied for both materials. In addition,since 2Ph-BTBT having the HOMO value of 5.6 eV was used as a p-typematerial (specifically, a p-type organic semiconductor material) of thephotoelectric conversion layer of Embodiment 1 and the HOMO (ionizationpotential) values of the compound (A), compound (B), compound (C), andcompound (D) were −5.4 eV or −5.5 eV, materials of the compound (A),compound (B), compound (C), and compound (D) satisfy all conditions ofthe above-described patent publication. However, the compound (A) andcompound (B) are found to be excellent in the external quantumefficiency and dark current, and particularly have 1-digit improvedafterimage time with respect to afterimage characteristics in comparisonto the compound (C) or the compound (D), and thus the compound (A) orthe compound (B) are found to be a more ideal material for theanode-side buffer layer. Although the reason for the dark currentreduced to about half (½) has not been elucidated, the compound (A) andthe compound (B) have one-digit or 2-digit higher hole mobility than thecompound (C) or the compound (D) as is apparent from Tables 1 and 2, andthe property is considered to have contributed to the improvement in theafterimage characteristics. In addition, the height of the hole mobilityis considered to be derived from the bithiophene skeleton in the motherskeleton on the basis of the contrast between compound (C) and compound(D). Moreover, by having a carbazole skeleton (i.e., by bindingcarbazole including nitrogen atoms in a side of the bithiopheneskeleton), the difference between the HOMO value of the material formingthe anode-side buffer layer and the HOMO value of the p-type materialforming the photoelectric conversion layer can be optimized(optimization of the energy level difference). That is, the HOMO valueof the anode-side buffer layer can approach, for example, −5.6 eV, andthe difference between the HOMO value of the material forming theanode-side buffer layer and the HOMO value of the p-type materialforming the photoelectric conversion layer can be set to be in the rangeof ±0.2 eV. In this manner, by using a derivative of the presentdisclosure in which thiophene and carbazole are combined for theanode-side buffer layer, dark current characteristics and afterimagecharacteristics which are problems to be solved for practicalapplications of organic imaging elements in addition to external quantumefficiency can be significantly improved. Further, since spectralcharacteristics of oligothiophene deteriorate when the degree ofpolymerization increases, the proper number of thiophenes to be used forthe anode-side buffer layer of an imaging element is 2 or smaller. Inaddition, there is a problem that the HOMO value of oligothiophene isshallow to around −5.2 eV.

FIG. 4 shows a conceptual diagram of an imaging apparatus ofEmbodiment 1. The imaging apparatus 100 of Embodiment 1 is formed of animaging area 111 in which the imaging elements 101 described above arearranged in a two-dimensional array on a semiconductor substrate (asilicon semiconductor substrate, for example), a vertical drive circuit112 as a drive circuit (peripheral circuit), a column signal processingcircuit 113, a horizontal drive circuit 114, an output circuit 115, adrive control circuit 116, etc. These circuits may be formed bywell-known circuits, and moreover, may be formed by using other circuitconfigurations (e.g., various circuits used in a conventional CCDimaging apparatus or CMOS imaging apparatus). Further, in FIG. 4, thereference number “101” of the stacked-type imaging element 101 is onlyshown in one row.

The drive control circuit 116 generates a clock signal and a controlsignal which are the basis of the operations of the vertical drivecircuit 112, the column signal processing circuit 113, and thehorizontal drive circuit 114 based on a vertical synchronization signal,a horizontal synchronization signal, and a master clock. Further, thegenerated clock signal and control signal are input to the verticaldrive circuit 112, the column signal processing circuit 113, and thehorizontal drive circuit 114.

The vertical drive circuit 112 is formed of, for example, a shiftregister, and selectively scans each imaging element 101 in the imagingarea 111 in the vertical direction in units of rows. Further, a pixelsignal (image signal) based on the current (signal) generated accordingto the amount of light received by each imaging element 101 is sent tothe column signal processing circuit 113 via the vertical signal lines117.

For example, the column signal processing circuit 113 is arranged foreach column of the imaging element 101, and signal processing for noiseremoval and signal amplification is performed on image signal outputfrom the imaging element 101 for one row in each imaging element 101 bya signal from a black reference pixel (not shown, but formed around theeffective pixel area). A horizontal selection switch (not shown) isprovided in the output stage of the column signal processing circuit 113so as to be connected to the horizontal signal line 118.

The horizontal drive circuit 114 is formed of, for example, a shiftregister, and sequentially selects each of the column signal processingcircuits 113 by sequentially outputting horizontal scanning pulses, andoutputs signals from each of the column signal processing circuits 113to the horizontal signal 118.

The output circuit 115 is output by performing signal processing on thesignals sequentially supplied from each of the column signal processingcircuits 113 via the horizontal signal line 118.

Here, since the organic photoelectric conversion layer itself functionsas a color filter, color separation can be performed without disposing acolor filter.

Embodiment 2

Although, Embodiment 2 is a modification of the imaging element ofEmbodiment 1, it relates to the stacked-type imaging element of thepresent disclosure and the imaging apparatus according to the secondaspect of the present disclosure. That is, the stacked-type imagingelement of Embodiment 2 (an imaging element with vertical spectroscopy)is formed by stacking at least one imaging element described inEmbodiment 1. In addition, the imaging apparatus of Embodiment 2 has aplurality of such stacked-type imaging elements. Specifically, thestacked-type imaging elements of Embodiment 2 has a configuration inwhich three imaging elements (three subpixels) including a blue imagingelement, a green imaging element, and a red imaging element described inEmbodiment 1 are stacked in the vertical direction as illustrated in theconceptual diagram of FIG. 5A. That is, the stacked-type imaging elementhaving a structure in which subpixels are stacked to form one pixel canbe obtained. The blue imaging element is positioned on the uppermostlayer, the green imaging element is positioned in the middle, and thered imaging element is positioned in the lowermost layer. However, astacking order is not limited thereto.

Alternatively, by providing the imaging elements described in Embodiment1 (a blue imaging element and a green imaging element in the illustratedexample) on a silicon semiconductor substrate and one or more imagingelements (imaging elements sensitive to red in the illustrate example)inside the silicon semiconductor substrate positioned below theaforementioned imaging elements as are illustrated in the conceptualdiagram of FIG. 5B, a stacked-type imaging element having the structurein which the imaging elements are stacked, that is, the structure inwhich subpixels are stacked to form one pixel, can be obtained. Further,although the imaging elements formed on the silicon semiconductorsubstrate are preferable for back surface illuminated type, they arepreferable for front surface illuminated type as well. Instead ofproviding the photoelectric conversion layer inside the siliconsemiconductor substrate, the imaging element can also be formed on thesemiconductor substrate using an epitaxial growth method, or formed on asilicon layer having a so-called SOI structure.

Further, in order not to disturb light reception of the imaging elementpositioned at the lower part in the stacked-type imaging element ofEmbodiment 2, an anode may be formed of, for example, a transparentconductive material, for example, ITO, and a cathode may also be formedof a transparent conductive material, for example, ITO in the imagingelements positioned at the upper part.

In the imaging apparatus of Embodiment 2 having the stacked-type imagingelements, separation of light such as blue, green, and red is notperformed using color filters, and imaging elements having sensitive tolight with different wavelengths are stacked in the light incidencedirection within the same pixel. Therefore, sensitivity and a pixeldensity per unit volume can be improved. In addition, since organicmaterials have high absorption coefficients, a film thickness of theorganic photoelectric conversion layer can be more thinned than aSi-based photoelectric conversion layer of the related art, and lightleakage from an adjacent pixel and limitation on the light incidenceangle can be alleviated. Furthermore, although a false color may begenerated in a Si-based imaging element of the related art since a colorsignal is produced by performing an interpolation process between threepixels, occurrence of false colors is curbed in the imaging apparatus ofEmbodiment 2 having such stacked-type imaging elements.

Embodiment 3

Embodiment 3 is a modification of Embodiment 1 and Embodiment 2. A morespecific schematic partial sectional view of an imaging element and astacked-type imaging element of Embodiment 3 is illustrated in FIG. 6,and an equivalent circuit diagram of the imaging element and thestacked-type imaging element Embodiment 3 is illustrated in FIG. 7. InEmbodiment 3, a semiconductor substrate (more specifically, a siliconsemiconductor layer) 70 is provided, and a photoelectric conversion unitis disposed on the semiconductor substrate 70. In addition, a controlunit provided in the semiconductor substrate 70 having a drive circuitconnected to a cathode 25 is included. Here, the light incidence surfaceof the semiconductor substrate 70 is assumed to be an upper part and theopposite side of the semiconductor substrate 70 to the light incidencesurface is assumed to be a lower part. A wiring layer 62 formed of aplurality of wires is provided at the lower pan of the semiconductorsubstrate 70. In addition, at least a floating diffusion layer FD₁ andan amplification transistor TR1 _(amp) constituting the control unit areprovided on the semiconductor substrate 70, and the cathode 25 isconnected to the gate part of the floating diffusion layer FD₁ and anamplification transistor TR1 _(amp). A reset transistor TR1 _(rst) and aselect transistor TR1 _(sel) constituting the control unit are furtherprovided on the semiconductor substrate 70. In addition, the floatingdiffusion layer FD₁ is connected to one of the source and drain regionsof the reset transistor TR1 _(rst), one of the source and drain regionsof the amplification transistor TR1 _(amp) is connected to one of thesource and drain regions of the select transistor TR1 _(sel), and theother of the source and drain regions of the select transistor TR1_(sel) is connected to a signal line VSL₁. These amplificationtransistor TR1 _(amp), reset transistor TR1 _(rst), and selecttransistor TR1 _(sel) constitute the drive circuit.

Specifically, the imaging element and stacked-type imaging element ofEmbodiment 3 are back surface illuminated type imaging element andstacked-type imaging element, and have a structure in which a first-typegreen imaging element of Embodiment 1 (hereinafter, referred to as“first imaging element”) having a first-type green photoelectricconversion layer which absorbs green light and having sensitivity togreen, a second-type conventional blue imaging element (hereinafter,referred to as “second imaging element”) having a second-typephotoelectric conversion layer which absorbs blue light and havingsensitivity to blue, and a second-type conventional red imaging element(hereinafter, referred to as “third imaging element”) having asecond-type photoelectric conversion layer which absorbs red light andhaving sensitivity to red are stacked. Here, the red imaging element(third imaging element) and the blue imaging element (second imagingelement) are provided in the semiconductor substrate 70, and the secondimaging element is located more closer to the light incident side ascompared to the third imaging element. Furthermore, the green imagingelement (first imaging element) is provided above the blue imagingelement (second imaging element). One pixel is formed by the stackedstructure of the first imaging element, the second imaging element, andthe third imaging element. No color filter is provided.

In the first imaging element, the cathode 25 is formed on the interlayerinsulating layer 81. The cathode-side buffer layer 24, the photoelectricconversion layer 2, and the anode-side buffer layer 22 are formed on thecathode 25, and the anode 21 is formed on the anode-side buffer layer22. Further, the cathode-side buffer layer 24, the photoelectricconversion layer 23, and the anode-side buffer layer 22 are illustratedas one layer. A protective layer 82 is formed on the entire surfaceincluding the anode 21, and an on-chip microlens 90 is provided on theprotective layer 82. The cathode 25 and the anode 21 are, for example,transparent electrodes formed of ITO. The photoelectric conversion layer23 is a layer including a known organic photoelectric conversionmaterial sensitive at least to green (e.g., an organic material such asquinacridone). In addition, the photoelectric conversion layer 23 mayfurther include a material layer appropriate for charge accumulation.That is, a material layer appropriate for charge accumulation may befurther formed between the cathode-side buffer layer 24 and the cathode25. The interlayer insulating layer 81 and the protective layer 82 areformed of a known insulating material (e.g., SiO₂ or SiN). Theanode-side buffer layer 22, the photoelectric conversion layer 23, andthe cathode-side buffer layer 24, and the cathode 25 are connected via aconnection hole 64 provided in the interlayer insulating layer 81.

An element separation region 71 is formed on the side of the firstsurface (front surface) 70A of the semiconductor substrate 70, and anoxide film 72 is formed on the first surface 70A of the semiconductorsubstrate 70. Moreover, a reset transistor TR1 _(rst), an amplificationtransistor TR1 _(amp) and select transistor TR1 _(sel) forming thecontrol unit of the first imaging element are provided on the side ofthe first surface of the semiconductor substrate 70, and a firstfloating diffusion layer FD₁ is further provided.

The reset transistor TR1 _(rst) is formed of a gate section 51, achannel forming region 51A and source drain regions 51B and 51C. Thegate section 51 of the reset transistor TR1 _(rst) is connected to thereset line RST₁, and the source/drain region 51C of one side of thereset transistor TR1 _(rst) also functions as the first floatingdiffusion layer FD₁, and the source/drain regions 51B of another side isconnected to the power supply V_(DD).

The cathode 25 is connected to a source/drain region 51C (first floatingdiffusion layer FD₁) of one side of the reset transistor TR1 _(rst) viaa connection hole 64 and a pad portion 63 provided in the interlayerinsulating layer 81, a contact hole portion 61 formed in thesemiconductor substrate 70 and the interlayer insulating layer 76, andthe wiring layer 62 formed in the interlayer insulating layer 76.

The amplification transistor TR1 _(amp) is formed of the gate section52, the channel forming region 52A and the source drain regions 52B and52C. The gate section 52 is connected to the cathode 25 and thesource/dram region 51C (first floating diffusion layer FD₁) of one sideof the reset transistor TR1 _(rst) through the wiring layer 62.Furthermore, the source/drain region 52B of one side shares a regionwith the source/drain region 51B of another side forming the resettransistor TR1 _(rst), and is connected to power supply V_(DD).

The select transistor TR1 _(sel) is formed of the gate section 53, thechannel forming region 53A and the source drain regions 53B and 53C. Thegate section 53 is connected to the select line SEL₁. Furthermore, thesource/drain region 53B of one side shares a region with thesource/drain region 52C of another side forming the amplificationtransistor TR1 _(amp), and the source/drain region 53C is connected tothe signal line (data output line) VSL₁.

The second imaging element includes an n-type semiconductor region 41provided in the semiconductor substrate 70 as a photoelectric conversionlayer. The gate section 45 of the transfer transistor TR2 _(trs) formedof the vertical transistor extends to the n-type semiconductor region 41and is connected to the transfer gate line TG₂. Furthermore, a secondfloating diffusion layer FD₂ is provided in a region 45C of thesemiconductor substrate 70 near the gate section 45 of the transfertransistor TR2 _(trs). Charges stored in the n-type semiconductor region41 are read out to the second floating diffusion layer FD₂ via atransfer channel formed along the gate section 45.

In the second imaging element, the reset transistor TR2 _(trs), theamplification transistor TR2 _(amp) and the select transistor TR2 _(sel)forming the control unit of the second imaging element are furtherprovided on the first surface side of the semiconductor substrate 70.

The reset transistor TR2 _(trs) is formed of the gate section, thechannel forming region and the source/drain region. The gate section ofthe reset transistor TR2 _(trs) is connected to the reset line RST₂, anda source/drain region of one side of the reset transistor TR2 _(trs) isconnected to the power supply V_(DD), and a source/drain region ofanother side also functions as a second a floating diffusion layer FD₂.

The amplification transistor TR2 _(amp) is formed of the gate section,the channel forming region and the source/drain region. The gate sectionis connected to a source/drain region (second floating diffusion layerFD₂) of another side of the reset transistor TR2 _(trs). Furthermore, asource/drain region of one side shares a region with a source/drainregion of one side forming the reset transistor TR2 _(trs), and isconnected to the power supply V_(DD).

The select transistor TR2 _(sel) is formed of the gate section, thechannel forming region and the source/drain region. The gate section isconnected to the select line SEL₂. Furthermore, a source/drain region ofone side shares a region with a source/drain region of another sideforming the amplification transistor TR2 _(amp), and a source/drainregion of another side is connected to the signal line (data outputline) VSL₂.

The third imaging element has an n-type semiconductor region 43 providedin the semiconductor substrate 70 as a photoelectric conversion layer.The gate section 46 of the transfer transistor TR3 _(trs) is connectedto the transfer gate line TG₃. Furthermore, a third floating diffusionlayer FD₃ is provided in a region 46C of the semiconductor substrate 70near the gate section 46 of the transfer transistor TR3 _(trs). Chargesstored in the n-type semiconductor region 43 are read out to the thirdfloating diffusion layer FD₃ via a transfer channel 46A formed along thegate section 46.

In the third imaging element, the reset transistor TR3 _(rst), theamplification transistor TR3 _(amp) and the select transistor TR3 _(sel)forming the control unit of the third imaging element are furtherprovided on the first surface side of the semiconductor substrate 70.

The reset transistor TR3 _(rst) is formed of the gate section, thechannel forming region and the source/drain region. The gate section ofthe reset transistor TR3 _(rst) is connected to the reset line RST₃, anda source/drain region of one side of the reset transistor TR3 _(rst) isconnected to the power supply V_(DD), and a source/drain region ofanother side also functions as the third floating diffusion layer FD₃.

The amplification transistor TR3 _(amp) is formed of the gate section,the channel forming region and the source/drain region. The gate sectionis connected to the source/drain region (third floating diffusion layerFD₃) of another side of the reset transistor TR3 _(rst). Furthermore, asource/drain region of one side shares a region with a source/drainregion of one side forming the reset transistor TR3 _(rst), and isconnected to the power supply V_(DD).

The select transistor TR3 _(sel) is formed of the gate section, thechannel forming region and the source/drain region. The gate section isconnected to the select line SEL₃. Furthermore, a source/drain region ofone side shares a region with a source/drain region of another sideforming the amplification transistor TR3 _(amp), and a source/drainregion of another side is connected to the signal line (data outputline) VSL₃.

Reset lines RST₁, RST₂ and RST₃, select lines SEL₁, SEL₂ and SEL₃, andtransfer gate lines TG₂ and TG₃ are connected to the vertical drivecircuit 112 forming the drive circuit, and signal lines (data outputlines) VSL₁, VSL₂ and VSL₃ are connected to a column signal processingcircuit 113 forming the drive circuit.

A p⁺ layer 44 is provided between the n-type semiconductor region 43 andthe surface 70A of the semiconductor substrate 70 to suppress generationof dark current. A p⁺ layer 42 is formed between the n-typesemiconductor region 41 and the n-type semiconductor region 43, and apart of the side surface of the n-type semiconductor region 43 issurrounded by the p⁺ layer 42. A p⁺ layer 73 is formed on the side ofthe back surface 70B of the semiconductor substrate 70, and an HfO₂ film74 and an insulating film 75 are formed in a portion between the p⁺layer 73 and the semiconductor substrate 70, where the contact holeportion 61 is to be formed. In the interlayer insulating layer 76,wirings are formed over a plurality of layers, but are omitted fromillustration.

The HfO₂ film 74 is a film having a negative fixed charge, andgeneration of dark current can be suppressed by providing such a film.Further, instead of the HfO₂ film, an aluminum oxide (Al₂O₃) film, azirconium oxide (ZrO₂) film, a tantalum oxide (Ta₂O₅) film, a titaniumoxide (TiO₂) film, a lanthanum oxide (La₂O₃) film, a praseodymium oxide(Pr₂O₃) film, a cerium oxide (CeO₂) film, a neodymium oxide (Nd₂O₃)film, a promethium oxide (Pm₂O₃) film, a samarium oxide (Sm₂O₃) film, aeuropium oxide (Eu₂O₃) film, a gadolinium oxide (Gd₂O₃) film, a terbiumoxide (TB₂O₃) film, a dysprosium oxide (Dy₂O₃) film, a holmium oxide(Ho₂O₃) film, a thulium oxide (Tm₂O₃) film, a ytterbium oxide (YB₂O₃)film, a lutetium oxide (Lu₂O₃) film, a yttrium oxide (Y₂O₃) film, ahafnium nitride film, an aluminum nitride film, a hafnium oxynitridefilm and an aluminum oxynitride film may be used. Examples of the filmforming method of these films include a CVD method, a PVD method and anALD method.

The imaging element and stacked-type imaging element of Embodiment 3 maybe manufactured by, for example, the following method. That is, first,an SOI substrate is prepared. Then, a first silicon layer is formed onthe surface of the SOI substrate by an epitaxial growth method, and a p⁺layer 73 and an n-type semiconductor region 41 are formed in the firstsilicon layer. Next, a second silicon layer is formed on the firstsilicon layer by an epitaxial growth method, and the element separationregion 71, the oxide film 72, the p⁺ layer 42, the n-type semiconductorregion 43, and the p⁺ layer 44 are formed on the second silicon layer.Furthermore, various transistors and the like forming the control unitof the imaging element are formed on the second silicon layer, and thewiring layer 62, an interlayer insulating layer 76, and various wiringsare further formed thereon, and then the interlayer insulating layer 76and the supporting substrate (not shown) are bonded to each other.Thereafter, the SOI substrate is removed to expose the first siliconlayer. Further, the surface of the second silicon layer corresponds tothe surface 70A of the semiconductor substrate 70, and the surface ofthe first silicon layer corresponds to the back surface 70B of thesemiconductor substrate 70. Furthermore, the first silicon layer and thesecond silicon layer are collectively referred to as the semiconductorsubstrate 70. Next, an opening for forming the contact hole portion 61is formed on the side of the back surface 70B of the semiconductorsubstrate 70, and the HfO₂ film 74, the insulating film 75 and thecontact hole portion 61 are formed, and the pad portions 63, theinterlayer insulating layer 81, the connection holes 64, and the cathode25 are further formed. Next, the anode-side buffer layer 22,photoelectric conversion layer 23, the cathode-side buffer layer 24, theanode 21, the protective layer 82, and the on-chip microlens 90 areformed. Accordingly, the imaging element and the stacked-type imagingelement of Embodiment 3 may be obtained.

The modified example-1 of the imaging element and stacked-type imagingelement of Embodiment 3 schematically shown in FIG. 8 are front surfaceilluminated type imaging element and stacked-type imaging element, andhave a structure in which a first-type green imaging element ofEmbodiment 1 (first imaging element) having a first-type greenphotoelectric conversion layer which absorbs green light and havingsensitivity to green, a second-type conventional blue imaging element(second imaging element) having a second-type photoelectric conversionlayer which absorbs blue light and having sensitivity to blue, and asecond-type conventional red imaging element (third imaging element)having a second-type photoelectric conversion layer which absorbs redlight and having sensitivity to red are stacked. Here, the red imagingelement (third imaging element) and the blue imaging element (secondimaging element) are provided in the semiconductor substrate 70, and thesecond imaging element is located more closer to the light incident sideas compared to the third imaging element. Furthermore, the green imagingelement (first imaging element) is provided above the blue imagingelement (second imaging element).

Various transistors forming the control unit are provided on the surface70A of the semiconductor substrate 70. Furthermore, the second imagingelement and the third imaging element are provided on the semiconductorsubstrate 70, and these imaging elements also may have the substantiallysame configuration and structure of the second imaging element and thethird imaging element described above.

The interlayer insulating layers 77 and 78 are formed on the surface 70Aof die semiconductor substrate 70, and the photoelectric conversion unit(the cathode 25, the cathode-side buffer layer 24, the photoelectricconversion layer 23, the anode-side buffer layer 22, and the anode 21)and the like forming the imaging elements are formed on the interlayerinsulating layer 78.

As described above, the configuration and structure of the imagingelement and the stacked-type imaging element of modified example-1 arethe same as those of the imaging element and the stacked-type imagingelement of Embodiment 3 except for being the front surface illuminatedtype imaging element and stacked-type imaging element, and thus detaileddescription will be omitted.

The modified example-2 of the imaging element and stacked-type imagingelement of Embodiment 3 schematically shown in FIG. 9 are back surfaceilluminated type imaging element and stacked-type imaging element, andhave a structure in which the first imaging element of the first type ofEmbodiment 1 and two second imaging elements of the second type arestacked. Further, modified example-3 of the imaging element ofEmbodiment 3 and stacked-type imaging element of which partial crosssectional views are shown in FIG. 10 are front surface illuminated typeimaging element and stacked-type imaging element, and have a structurein which the first imaging element of the first type of Embodiment 1 andtwo second imaging elements of the second type are stacked. Here, thefirst imaging element absorbs primary color of light, and the secondimaging element absorbs complementary color of light. Alternatively, thefirst imaging element absorbs white light and the second imaging elementabsorbs infrared light.

The modified example-4 of the imaging element of Embodiment 3 of which aschematic partial sectional view is shown in FIG. 11 is a back surfaceilluminated type imaging element, and is formed of the first imagingelement of the first type of Embodiment 1. Furthermore, the modifiedexample-5 of the imaging element of Embodiment 3 of which a schematicpartial sectional view is shown in FIG. 12 is a front surfaceilluminated type imaging element, and is formed of the first imagingelement of the first type of Embodiment 1. Here, the first imagingelement is formed of three types of imaging elements including animaging element absorbing red light, an imaging element absorbing greenlight and an imaging element absorbing blue light. Moreover, the imagingapparatus according to the first aspect of the present disclosure isformed of a plurality of these imaging elements. An example of thearrangement of a plurality of the imaging elements includes a Bayerarray. Color filters for performing spectral division of blue, green,and red are provided as necessary at the light incident side of eachimaging element.

Further, the form in which two first-type imaging element of Embodiment1 are stacked (i.e., form in which two photoelectric conversion unitsare stacked and control units of two imaging elements are provided onsemiconductor substrate), or, the form in which three first-type imagingelement are stacked (i.e., form in which three photoelectric conversionunits are stacked and control units of three imaging elements areprovided on semiconductor substrate) may be adopted instead of providingone imaging first-type element. An example of a stacked structure of thefirst-type imaging element and the second-type imaging element isexemplified in the following table 3.

TABLE 3 Reference First type Second type drawing Back surface 1 2 FIG. 1illuminated Green Blue + red FIG. 8 type and front 1 1 FIG. 9 surfacePrimary color Complementary color FIG. 10 illuminated 1 1 type WhiteInfrared ray 1 0 FIG.11 Blue or green or red FIG. 12 2 2 Green +infrared light Blue + red 2 1 Green + Blue Red 2 0 White + Infraredlight 3 2 Green + blue + red Blue-green (emerald color) + infrared light3 1 Green + blue + red Infrared light 3 0 Blue + green + red

FIG. 13 is a conceptual diagram of an example in which an imagingapparatus 201 formed of the imaging element and stacked-type imagingelement of the present disclosure is used in an electronic device(camera) 200. The electronic device 200 includes the imaging apparatus201, an optical lens 210, a shutter device 211, a drive circuit 212, anda signal processing circuit 213. The optical lens 210 forms an imagelight (incident light) from a subject as an image on an imaging surfaceof the imaging apparatus 201. Thus, signal charges are accumulated inthe imaging apparatus 201 for a given period. The shutter device 211controls a light irradiation period and a light shielding period for theimaging apparatus 201. The drive circuit 212 supplies a drive signal forcontrolling a transfer operation or the like of the imaging apparatus201 and a shutter operation of the shutter device 211. A signal of theimaging apparatus 201 is transferred in accordance with the drive signal(timing signal) supplied from the drive circuit 212. The signalprocessing circuit 213 performs various kinds of signal processing. Avideo signal subjected to the signal processing is stored in a storagemedium such as a memory or is output to a monitor. Since miniaturizationof a pixel size in the imaging apparatus 201 and transfer efficiency areimproved in the electronic device 200, the electronic device 200 inwhich an improvement in pixel characteristics is achieved can beobtained. The electronic device 200 to which the imaging apparatus 201can be applied is not limited to a camera and can also be applied to animaging apparatus such as a digital still camera or a camera module fora mobile device such as a mobile phone.

The present disclosure has been described above according to preferredembodiments, but is not limited to these embodiments. The structures,the configurations, the manufacturing conditions, the manufacturingmethods, and the used materials of the imaging element, the stacked-typeimaging element, and the imaging apparatus described in the embodimentsare exemplary and can be appropriately changed. In a case in which aphotoelectric conversion element of the present disclosure is set tofunction as a solar cell, light may be irradiated to a photoelectricconversion material layer with no voltage applied between the anode andthe cathode.

Additionally, the present technology may also be configured as below.

[A01] <<Imaging Element: First Aspect>>

An imaging element which is formed by sequentially stacking at least ananode, an anode-side buffer layer, a photoelectric conversion layer, anda cathode,

in which the anode-side buffer layer includes a material havingstructural formula (1):

in which thiophene and carbazole are combined,

where X₁, X₂, X₃, and X₄ are each independently a group consisting of analkyl group, an aryl group, an arylamino group, an aryl group having anarylamino group as a substituent, and a carbazolyl group, and may or maynot have a substituent,

the aryl group and the aryl group having an arylamino group as asubstituent are an aryl group selected from a group consisting of aphenyl group, a biphenyl group, a naphthyl group, a naphthyl phenylgroup, a phenyl naphthyl group, a tolyl group, a xylyl group, aterphenyl group, an anthracenyl group, a phenanthryl group, a pyrenylgroup, a tetracenyl group, a fluoranthenyl group, a pyridinyl group, aquinolinyl group, an acridinyl group, an indole group, an imidazolegroup, a benzimidazole group, and a thienyl group, and

the alkyl group may be an alkyl group selected from a group consistingof a methyl group, an ethyl group, a propyl group, a butyl group, apentyl group, and a hexyl group, or a linear or branched alkyl group.

[A02] <<Imaging Element: Second Aspect>>

An imaging element which is formed by sequentially stacking at least ananode, an anode-side buffer layer, a photoelectric conversion layer, anda cathode,

in which the anode-side buffer layer includes a material havingstructural formula (2):

in which thiophene and carbazole are combined,

where Y₁, Y₂, Y₃, Y₄, Y₅, Y₆, Y₇, and Y₈ are each independently a groupconsisting of an alkyl group, an aryl group, an arylamino group, an arylgroup having an arylamino group as a substituent, and a carbazolylgroup, and may or may not have a substituent,

the aryl group and the aryl group having an arylamino group as asubstituent are an aryl group selected from a group consisting of aphenyl group, a biphenyl group, a naphthyl group, a naphthyl phenylgroup, a phenyl naphthyl group, a tolyl group, a xylyl group, aterphenyl group, an anthracenyl group, a phenanthryl group, a pyrenylgroup, a tetracenyl group, a fluoranthenyl group, a pyridinyl group, aquinolinyl group, an acridinyl group, an indole group, an imidazolegroup, a benzimidazole group, and a thienyl group, and

the alkyl group may be an alkyl group selected from a group consistingof a methyl group, an ethyl group, a propyl group, a butyl group, pentylgroup, and a hexyl group, or a linear or branched alkyl group,

[A03] <<Imaging Element: Third Aspect>>

An imaging element which is formed by sequentially stacking at least ananode, an anode-side buffer layer, a photoelectric conversion layer, anda cathode,

in which the anode-side buffer layer includes a material havingstructural formula (3):

where Ar₁, Ar₂, Ar₃, Ar₄, Ar₅, Ar₆, Ar₇, and Ar₈ are each independentlyan aryl group selected from the group consisting of a phenyl group, abiphenyl group, a naphthyl group, a naphthyl phenyl group, a phenylnaphthyl group, a tolyl group, a xylyl group, a terphenyl group, ananthracenyl group, a phenanthryl group, a pyrenyl group, a tetracenylgroup, a fluoranthenyl group, a pyridinyl group, a quinolinyl group, anacridinyl group, an indole group, an imidazole group, a benzimidazolegroup, and a thienyl group.

[A04]

The imaging element according to [A03], in which the anode-side bufferlayer includes a material having structural formula (4) or structuralformula (5):

in which thiophene and carbazole are combined.[A05]

The imaging element according to any one of [A01] to [A04], in which thedifference between a HOMO value of the material forming the anode-sidebuffer layer and a HOMO value of a p-type material forming thephotoelectric conversion layer is in the range of ±0.2 eV.

[A06]

The imaging element according to [A05], in which the HOMO value of thep-type material forming the photoelectric conversion layer is a valuefrom −5.6 eV to −5.7 eV.

The imaging element according to any one of [A01] to [A06], in whichcarrier mobility of the material forming the anode-side buffer layer ishigher than or equal to 5×10⁻⁶ cm²/V·s.

[A08]

The imaging element according to any one of [A01] to [A07], in which anabsorption spectrum of the material forming the anode-side buffer layerhas an absorption maximum at a wavelength of 425 nm or lower.

[A09]

The imaging element according to any one of [A01] to [A08], in which theanode and the cathode are formed of a transparent conductive material.

[A10]

The imaging element according to any one of [A01] to [A08], in which oneof the anode and the cathode is formed of a transparent conductivematerial and the other is formed of a metal material.

[B01] <<Stacked-Type Imaging Element>>

A stacked-type imaging element formed by stacking at least one imagingelement according to any one of [A01] to [A10].

[C01] <<Imaging Apparatus: First Aspect>>

An imaging apparatus including:

a plurality of imaging elements according to any one of [A01] to [A10].

[C02] <<Imaging Apparatus: Second Aspect>>

An imaging apparatus including:

a plurality of stacked-type imaging elements according to [B01].

[D01] <<Photoelectric Conversion Element>>

An imaging element which is formed by sequentially stacking at least ananode, an anode-side buffer layer, a photoelectric conversion layer, anda cathode,

in which the anode-side buffer layer includes a material havingstructural formula (1) or structural formula (2) or structural formula(3) or structural formula (4): in which thiophene and carbazole arecombined.

[E01] <<Manufacturing Method of the Imaging Element>>

A manufacturing method of an imaging element which is formed bysequentially stacking at least an anode, an anode-side buffer layer, aphotoelectric conversion layer, and a cathode, in which the anode-sidebuffer layer includes a material having structural formula (1),structural formula (2), structural formula (3), structural formula (4),or structural formula (5) in which thiophene and carbazole are combined,and the anode-side buffer layer is formed by using a physical vapordeposition method.

[E02] The manufacturing method of the imaging element described in [E01]in which the photoelectric conversion layer is also formed using thephysical vapor deposition method.

[E03]

The manufacturing method of the imaging element described in [E01] or[E02], in which the difference between a HOMO value of the materialforming the anode-side buffer layer and a HOMO value of a p-typematerial forming the photoelectric conversion layer is in the range of+0.2 eV.

[E04]

The manufacturing method of the imaging element described in [E03], inwhich the HOMO value of the p-type material forming the photoelectricconversion layer is a value from −5.6 eV to −5.7 eV.

[E05]

The manufacturing method of the imaging element described in any one of[E01] to [E04], in which carrier mobility of the material forming theanode-side buffer layer is higher than or equal to 5×10⁻⁶ cm²/V·s.

[E06]

The manufacturing method of the imaging element described in any one of[E01] to [E05], in which an absorption spectrum of the material formingthe anode-side buffer layer has an absorption maximum at a wavelength of425 nm or lower.

[E07]

The manufacturing method of the imaging element described in any one of[E01] to [E06], in which the anode and the cathode are formed of atransparent conductive material.

The manufacturing method of the imaging element described in any one of[E01] to [E07], in which one of the anode and the cathode is formed of atransparent conductive material and the other is formed of a metalmaterial.

REFERENCE SIGNS LIST

-   11 imaging element-   20 substrate-   21 anode-   22 anode-side buffer layer-   23 organic photoelectric conversion layer-   24 cathode-side buffer layer-   25 cathode-   31 insulating layer-   41 n-type semiconductor region forming second imaging element-   43 n-type semiconductor region forming third imaging element-   42, 44, 73 p⁺ layer-   FD₁, FD₂, FD₃, 45C 46C floating diffusion layer-   TR1 _(amp) amplification transistor-   TR1 _(rst) reset transistor-   TR1 _(sel) select transistor-   51 the gate section of the reset transistor TR1 _(rst)-   51A channel forming region of reset transistor TR1 _(rst)-   51B, 51C source/drain regions of reset transistor TR1 _(rst)-   52 gate section of amplification transistor TR1 _(amp)-   52A channel forming region of amplification transistor TR1 _(amp)-   52B, 52C source/drain regions of amplification transistor TR1 _(amp)-   53 gate section of select transistor TR1 _(sel)-   53A channel forming region of select transistor TR1 _(sel)-   53B, 53C source/drain regions of select transistor TR1 _(sel)-   TR2 _(trs) transfer transistor-   45 gate section of transfer transistor-   TR2 _(trs) reset transistor-   TR2 _(amp) amplification transistor-   TR2 _(sel) select transistor-   TR3 _(trs) transfer transistor-   46 gate section of transfer transistor-   TR3 _(rst) reset transistor-   TR3 _(amp) amplification transistor-   TR3 _(sel) select transistor-   V_(DD) power supply-   RST₁, RST₂, RST₃ reset line-   SEL₁, SEL₂, SEL₃ select line-   117, VSL₁, VSL₂, VSL₃ signal line-   TG₂, TG₃ transfer gate line-   V_(OA), V_(OT), V_(OU) wiring-   61 contact hole portion-   62 wiring layer-   63 pad portion-   64 connection hole-   70 semiconductor substrate-   70A first surface (front surface) of semiconductor substrate-   70B second surface (back surface) of semiconductor substrate-   71 element separation region-   72 oxide film-   74 HfO₂ film-   75 insulating film-   76 interlayer insulating layer-   77, 78, 81 interlayer insulating layer-   82 protective layer-   90 on-chip microlens-   100 imaging apparatus-   101 stacked-type imaging element-   111 imaging area-   112 vertical drive circuit-   113 column signal processing circuit-   114 horizontal drive circuit-   115 output circuit-   116 drive control circuit-   118 horizontal signal line-   200 electronic device (camera)-   201 imaging apparatus-   210 optical lens-   211 shutter device-   212 drive circuit-   213 signal processing circuit

What is claimed is:
 1. An imaging element which is formed bysequentially stacking at least an anode, an anode-side buffer layer, aphotoelectric conversion layer, and a cathode, wherein the photoelectricconversion layer comprises a thienoacene-based p-type material, whereinthe anode-side buffer layer comprises a material having structuralformula (1):

in which thiophene and carbazole are combined, where X₁, X₂, X₃, and X₄are each independently an arylamino group and may or may not have asubstituent.
 2. The imaging element according to claim 1, wherein adifference between a HOMO value of the material forming the anode-sidebuffer layer and a HOMO value of the thienoacene-based p-type materialis in a range of ±0.2 eV.
 3. The imaging element according to claim 2,wherein the HOMO value of the p-type material forming the photoelectricconversion layer is a value from −5.6 eV to −5.7 eV.
 4. The imagingelement according to claim 1, wherein a carrier mobility of the materialforming the anode-side buffer layer is higher than or equal to 5×10⁻⁶cm²/V·s.
 5. The imaging element according to claim 1, wherein anabsorption spectrum of the material forming the anode-side buffer layerhas an absorption maximum at a wavelength of 425 nm or lower.
 6. Theimaging element according to claim 1, wherein the anode and the cathodeare formed of a transparent conductive material.
 7. The imaging elementaccording to claim 1, wherein one of the anode and the cathode is formedof a transparent conductive material and the other is formed of a metalmaterial.
 8. A stacked-type imaging element which is formed by stackingat least one of the imaging elements according to claim
 1. 9. An imagingapparatus comprising: a plurality of imaging elements according toclaim
 1. 10. An imaging apparatus comprising: a plurality ofstacked-type imaging elements according to claim
 8. 11. The imagingelement according to claim 1, wherein the photoelectric conversion layerfurther comprises a second p-type material and/or a n-type material,wherein the second p-type is selected from the group consisting of anaphthalene derivative, an anthracene derivative, a phenanthrenederivative, a pyrene derivative, a perylene derivative, a tetracenederivative, a pentacene derivative, a quinacridone derivative, atriallylamine derivative, a carbazole derivative, a picen derivative, achrysen derivative, a fluoranthene derivative, a phthalocyaninederivative, a subphthalocyanine derivative, a subporphyrazinederivative, a metal complex having a heterocyclic compound as a ligand,a polythiophene derivative, a polybenzothiadiazole derivative, apolyfluorene derivative is included, and combinations thereof, andwherein the n-type material is selected from the group consisting offullerene, a fullerene derivative, a heterocyclic compound containing anitrogen atom, an oxygen atom, and a sulfur atom, a pyridine derivative,a pyrazine derivative, a pyrimidine derivative, a triazine derivative, aquinoline derivative, a quinoxaline derivative, an isoquinolinederivative, an acridine derivative, a phenazine derivative, abenanthroline derivative, a tetrazole derivative, a pyrazole derivative,an imidazole derivative, a thiazole derivative, an oxazole derivative,an imidazole derivative, a benzimidazole derivative, a penzotriazolederivative, a benzoxazole derivative, a benzoxazole derivative, acarbazole derivative, a benzofuran derivative, a dibenzofuranderivative, a subporphyrazine derivative, a polyphenylene vinylenederivative, a polybenzothiadiazole derivative, a polyfluorenederivative, a subphthalocyanine derivative, and combinations thereof.12. The imaging element according to claim 1, wherein the photoelectricconversion layer includes an inorganic material selected from the groupconsisting of crystal silicon, amorphous silicon, microcrystallinesilicon, crystalline selenium, amorphous selenium, CIGS (CuInGaSe), CIS(CuInSe₂), CuInS₂, CuAlS₂, CuAlSe₂, CuGaS₂, CuGaSe₂, AgAlS₂, AgAlSe₂,AgInS₂, AgInSe₂, GaAs, InP, AlGaAs, InGaP, AlGaInP, InGaAsP, CdSe, CdS,In₂Se₃, In₂S₃, Bi₂Se₃, Bi₂S₃, ZnSe, ZnS, PbSe, PbS, a quantum dot formedthereof, and combinations thereof.
 13. The imaging element according toclaim 1, wherein the thienoacene-based p-type material comprises one ormore of a thiophene derivative, a thienothiophene derivative, abenzothiophene derivative, a benzothienobenzothiophene (BTBT)derivative, a dinaphthothienothiophene (DNTT) derivative, adiantrasenothienothiophene (DATT) derivative, a benzobisbenzothiophene(BBBT) derivative, a thienobis benzothiophene (TBBT) derivative, adibenzothienobisbenzothiophene (DBTBT) derivative, adithienobenzodithiophene (DTBDT) derivative, a dibenzothienodithiophene(DBTDT) derivative, a benzodithiophene (BDT) derivative, anaphthodithiophene (NDT) derivative, an anthracenodithiophene (ADT)derivative, a tetrasenodithiophene (TDT) derivative, and apentasenodithiophene (PDT) derivative.
 14. The imaging element accordingto claim 1, wherein the imaging element further comprises a cathode-sidebuffer layer interposed between the photoelectric conversion layer andthe cathode, wherein a work function of a material of the cathode sidebuffer layer is greater than a work function of the material of theanode side buffer layer.
 15. The imaging element according to claim 1,wherein each of X₁, X₂, X₃, and X₄ of the material having structuralformula (1) is a 3,6-bis(diphenylaminyl)carbazole group.
 16. An imagingelement which is formed by sequentially stacking at least an anode, ananode-side buffer layer, a photoelectric conversion layer, and acathode, wherein the photoelectric conversion layer comprises athienoacene-based p-type material, wherein the anode-side buffer layercomprises a material having structural formula (2):

in which thiophene and carbazole are combined, where Y₁, Y₂, Y₃, Y₄, Y₅,Y₆, Y₇, and Y₈ are each independently a group consisting of an alkylgroup, an aryl group, an arylamino group, an aryl group having anarylamino group as a substituent, and a carbazolyl group, and may or maynot have a substituent, the aryl group and the aryl group having anarylamino group as a substituent are an aryl group selected from a groupconsisting of a phenyl group, a biphenyl group, a naphthyl group, anaphthyl phenyl group, a phenyl naphthyl group, a tolyl group, a xylylgroup, a terphenyl group, an anthracenyl group, a phenanthryl group, apyrenyl group, a tetracenyl group, a fluoranthenyl group, a pyridinylgroup, a quinolinyl group, an acridinyl group, an indole group, animidazole group, a benzimidazole group, and a thienyl group, and thealkyl group may be an alkyl group selected from the group consisting ofa methyl group, an ethyl group, a propyl group, a butyl group, a pentylgroup, and a hexyl group, or a linear or branched alkyl group.
 17. Animaging element which is formed by sequentially stacking at least ananode, an anode-side buffer layer, a photoelectric conversion layer, anda cathode, wherein the photoelectric conversion layer comprises athienoacene-based p-type material, wherein the anode-side buffer layercomprises a material having structural formula (3):

where Ar₁, Ar₂, Ar₃, Ar₄, Ar₅, Ar₆, Ar₇, and Ar₈ are each independentlyan aryl group selected from the group consisting of a phenyl group, abiphenyl group, a naphthyl group, a naphthyl phenyl group, a phenylnaphthyl group, a tolyl group, a xylyl group, a terphenyl group, ananthracenyl group, a phenanthryl group, a pyrenyl group, a tetracenylgroup, a fluoranthenyl group, a pyridinyl group, a quinolinyl group, anacridinyl group, an indole group, an imidazole group, a benzimidazolegroup, and a thienyl group.
 18. The imaging element according to claim17, wherein the anode-side buffer layer includes a material havingstructural formula (4) or structural formula (5):

in which thiophene and carbazole are combined.
 19. A manufacturingmethod of an imaging element which is formed by sequentially stacking atleast an anode, an anode-side buffer layer, a photoelectric conversionlayer, and a cathode, wherein the photoelectric conversion layercomprises a thienoacene-based p-type material, wherein the anode-sidebuffer layer comprises a material having structural formula (1):

in which thiophene and carbazole are combined, and the anode-side bufferlayer is formed by using a physical vapor deposition method, where X₁,X₂, X₃, and X₄ are each independently an arylamino group and may or maynot have a substituent.